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Thread: My newest project - AR-15 in 6x45

  1. #1

    My newest project - AR-15 in 6x45

    Hello all!!

    I wanted to share my newest project that I have embarked on.

    Those of you that know me, know that I have been reloading for the better part of 25 years.

    Those same people will know that latest and longest standing addiction is building AR’s in all their configurations!!

    I have built fully functional and reliable AR-15's in many conventional calibers including 223/5.56 Nato, 7.62x39, 300 BlackOut, 6.8 spc, 6.5 Grendel.

    I have also built several AR's in 308 including both the DPMS/SR-25 pattern and the Armalite AR-10 B pattern in 308/7.62 Nato

    Along the way, I have reloaded for all of them. My latest adventure in to AR’s is to try some less conventional calibers. To that end I want to build with the 6x45 Caliber (also known as 6mm-223). I have heard a lot of good things about this cartridge, and I am look forward to working with it. For those that are unfamiliar, its basically a 223 necked up to 6mm. Weight for weight the 6mm bullets seem to have a higher BC than its 223 counter parts, and I have heard the the 6x45 hits quite hard for such a diminutive cartridge.

    To that end, a key piece of the puzzle arrived today, my barrel !!

    Looks like this:

    This is a unique item. This barrel started life as a 243 Sako Take-off barre with microgroove rifling that has been re-worked into a 20" Hbar profile for 6x45.

    To be honest I a really quite impressed!!

    For thoses that are interested Contour specs are as follows:
    • 20 1/4" long (20 3/4" including barrel extension)
    • Extension was new with Extension pin installed.
    • 0.915" diameter in front of the bbl. extension, for 2.35"
    • then 0.813" to the gas block shoulder
    • Shoulder is 12" from the bbl. extension (means a Rifle length gas system)
    • 0.751" diameter at gas block journal with a 2" length
    • Balance of barrel in front of Journal is 0.697"
    • Muzzle is threaded 1/2-28 for .792".
    • gas port is currently drilled as 1/16 (0.0625") Pilot hole.
    • Rate of twist looks like 1:10
    • total round count is unsure (but I had a look and what I saw looks really good!!)
    • In the white. Could be finished with a coating as is, or blasted and parked.

    For the money I paid I am over all really pleased. I want to open up the gas port to 0.090 and start with load development and experimentation there.

    My research has shown that A port size of 0.069-0.090 is standard for a 20" rifle 223/5.56 Nato. I want to start on the high side as the 6x45 is a some what lower preasured cartride when compared to 223.

    For example:

    .223 70 Gr. SPR SP Max 26.5 gr BLC-2 2954 fps 50,800 CUP

    6x45 70 Gr. HDY SP Max 29.5 gr BLC-2 3038 fps 48,500 CUP

    6x45 80 GR SPR SP Max 27.5 gr BLC-2 2846 fps 49,000 CUP

    As for opening up the gas port, I would prefer to use a drill press, but don't have one right now.

    Ah well, we will see how this progresses.

    Thanks for taking the time to read my post and I look forward to all your constructive comments


    Last edited by AbHobbyist; 12-27-2017 at 09:50 PM. Reason: making picture links work

  2. #2
    Adjustable gas block? I've never tried one, but it might prove useful in this case.

    Interesting project. I look forward to seeing the rest of the parts come together.

  3. #3

    Thank you for your interest.

    I thought about an adjustable gas block, however at this point I think the issue will be getting enough gas to go through the system.

    Should I make the port to large, then being able to limit or adjust the gas flow might make one of these worth while.

    As for the rest of the parts

    The lower I am going to be using my precision lower. Its a Tactical Innovations lower with a Geissele SSA-E fire control group in it , and A-1 style butt stock with an AS butt plate, or PRS. I have not decided yet.

    I have a run of the mill Cerro Forge flat top upper, with a new Semi-auto bolt and carrier group, and a Left handed charge handle with tac-latch. Probably add a Zombie Hunter just cover just for fun.

    I hope to have some additional pictures for you as things progress.

    Please keep the questions and thought coming, I find them very helpful in this process, and we can all learn together!!



  4. #4
    Tagging along with lots of interest and look forward to the results.

  5. #5

    Good morning!!

    I had time this weekend, and spent it working on my 6x45 project. I was able to spent time both at the reloading and work bench. There is a lot of ground to cover so I am going to do my best to split what I have to report into two sections. First I will talk about the progress at the reloading bench, and the we will chat about what happened at the work bench.



    The first issue was to make some good 6x45 brass.

    I was able to get my hands on some Redding dies in 6x45. These are the preferred dies in this caliber as the expander button is tapered and is very easy on the brass. Further it makes forming easy as you just lube the cases as normal, and run them through the die, and pesto, you have formed 6x45 brass.

    When choosing which brass to use, my research showed that generally speaking its best to stay away from military brass, as its thicker, is more stiff, and does not form as easily. The exception to this rule seem to be Norinko brass (usually had the JC ## head stamp). This brass does not seem to have crimped in primers, and I have successfully used this brass to make some great 300 Black Out cases.

    As such I tried some Norinco Federal (black box), and Winchester brass. I formed 5 cases of each, trimmed to length (1.75" the same as 223), champhered and de-burred the case mouth (inside and out), and then tried them for fit in my 6x45 barrel. Needless to say, the Winchester was the best fit, with the Norinco brass a close second, and the Federal brass needing two sizings to fit properly. As such I decided to use the Winchster brass.

    It is of interest to note that none the winchester brass required trimming, and all were sightly short. I suppose that one could learn from this that opening the mouth or “sizing up” shortens the case. Note: If I can remember, I will mike some with my calipers and add the measurement here.

    I then used my RCBS Auto Priming Tool to prime the cases with Dominion (Canada Ammo) Small rifle primers. The final result looks like this

    Test loads

    Powder choice

    There are several powders that are suitable for 6x54. Some that come to mind are

    Reloader 7
    Win 748

    Base on my research, in AR’s, many cycling issues are cause by using powders that are on the fast burring side of the spectrum. As the barrel I am using is 20" long, I felt that using a slower burning powder may give me an advantage.

    I have had good success in 223/5.56 Nato (both in reliable function and accuracy) using H4895 in barrels 20 inches an longer. As it is on the slower side of the spectrum, and I have an ample supply on hand, that is what I am going to start with.


    The projectiles in 6mm/0.2432 that I have on hand are 55 grin Nosler Balistic tip (400 count) and 70 Grain Sierra Blitz kings. There were left over from my work with the 243 Win bolt gun, and are representative of the weights I wanted to use.

    Its important to keep in mind that I will be using these in an AR-15, and as such I am stuck with a maximum magazine length (COL) of 2.260". This has implications for bullet weight, as the max bullet weight that I can use with you impeeding case powder capacity will be in th e85-87 grain range. This is fine as the 1-10 twist I have should be able to stabilize that weight.

    I was not really able to find data for 55 grain projectiles. However I did find the following bit of information that I already shared with regards to preasure, but I think it bears repeating:

    the 6x45 is a some what lower pressured cartridge when compared to 223. For example:

    .223 70 Gr. SPR SP Max 26.5 gr BLC-2 2954 fps 50,800 CUP

    6x45 70 Gr. HDY SP Max 29.5 gr BLC-2 3038 fps 48,500 CUP

    6x45 80 GR SPR SP Max 27.5 gr BLC-2 2846 fps 49,000 CUP
    As such I felt comfortable simply inferring my load data using 5.56 Nato data with projectiles of the same weight. As such my test load data/ladder looks as follows:

    I started at 22.0 grains and worked my way up to 25.0 grains in 0.5 grain increments

    Now on the Hodgon web site there is published data for 70 grain projectiles, and I simply used it. . As such my test load data/ladder looks as follows:

    One interesting note, is that the loads for the 70 grain projectiles are higher/greater than the load for the 55grain projectiles. Perhaps the difference is in the fact that one is specifically for AR’s and the other may be for bolt guns. I will defiantly pay attention for pressure signs when shooting these test loads

    Putting the reloads together

    Normally this is pretty straight forward, but I did encounter one snag. The Redding dies are normally excellent, however the # 6 seating plug that came with these dies would only allow me to seat my 55 Grain Nosler BT to 2.305" when turned all the way dow, and the die adjusted to just contact the seating ram of my old school RCBS Rock Chucker Press. To get down to the desired 2.260" I had to use the #25 seating plug out of my redding 223 dies. This is not really that big a deal, but considering how much I spent on these dies (they came from Prophet River here in Alberta), and extra seating stem should have been included. A call to Redding customer service may be in order.

    Final product

    Well the rest of the reloading session went with out incident, and the following is a picture of the final results

    The cases on top of the ammo boxes are the dummy carbides I made up so I can quickly set seating depth the next time I reload the same projectile

    For interest sake, here is a comparison picture of some 223/5.56 nato, 308 win, and 6x45

    From left to right: 223/5.56 Nato - 69 gr hpbt, 60gr Vmax, 55grn Blitzking, 55 FMJ emty 223 case
    Center: 308 win 175 SMK

    From Right to left: 6x45 70 Gr Sierra BlitzKing, 55gr Nosler BT, Emty 6x45 case

    Well that is enough for now.

    Stay tuned for my time at the work bench this weekend.


    Last edited by AbHobbyist; 12-27-2017 at 09:56 PM.

  6. #6
    At the work bench

    As promised this is the second installment of my working with the 6x45. In this post I hope to go over some of the issues I encountered when building this AR-15.

    The gas port

    As previously stated the I was very pleased with the barrel that I found in 6x45. The biggest issue was the proper diameter of the gas port. I must have agonized over this for more than a week.

    If you research this you will find gas port size (depending on barrel lenth) any wear from 0.069" all the way to the huge 0.101". Further, there comes the issue of proper port placment, and making sure its drilled square and level.

    The first thing that I did correctly was to have the barrel maker drill a 1/16" (0.0625) pilot hole. He has the equipment to ensure proper placement and alignment. This way, any subsequent drilling would simply follow the path or the pilot hole

    Now what some die hard will do, is take a set of block, clamps, and battery operated drills to the range. Settle on a load, and then shoot, and open up the gas port until they get reliable function.

    To that end, a very good mechanic friend of mine, kindly lent me the following set of drill bits.

    However, I just don’t have the time or patients to do that kind of thing.

    The more I researched, the more I was convinced that a larger port that 223/5.56 Nato would be required. In the end I settled on a port size of 0.093.

    I use my cordless drill along with good gun oil, and drilled the port in two stages. I first enlarged it to 0.076, then to 0.093. I then used the 0.098 to chambfer the entry point of the port ever so slightly. I also inserted an old aluminum 22 cal cleaning rod into the barrel, just to make sure I did not drill to deeply. I clamped everything in my bench vise, leveled it to the best if my ability, and supported the area under the gas port where I was drilling. This is what my poor-mans set up looked like:

    I have to say, these bits are really excellent, hard and sharp!! The drilling took much less time than I expected. Unfortunately I did not take a picture of the final port (my bad)

    Once the port was done, I then proceeded to put the rest of the rifle together. However there is one more item worth noting

    Muzzle treatment

    While note uncommon in hunting rifles, 6mm/.243 is somewhat unusual for an AR-15. Further with “lack of gas” for proper functioning, especially with an indeterminate gas port size, I wanted to use a muzzle treatment that would aid in gas retention.

    I settled on a linear comp by Kaw Valley (it helped that I has one in the bin and my barrel is threaded 1/2x28). This is what mine looks like

    Great, but what size exit port is required?? Well if you visit the Brownells website, and look at muzzle breaks, you will find that most breaks need an exit hole 0.020 over bore diameter.

    So the math looks like this: 0.243 + 0.020 = 0.263

    So I took my calipers and measured the exit hole on the comp, and it measured 0.265 Great so no enlargement of the exit hole will be required.

    This is what the final product looks like:

    Specs are as follows:


    • Barrel please see above post for spes
    • Kaw Valley Linear Comp (exit port miked to 0.265)
    • Armalite Squeeze style railed gas block
    • Good used Rifle length gas tube with New pin
    • Old School Samson Star R rifle length Quad Rail
    • Harris S 9-13 Swivel bi-pod with Generic Bi-pod adaptor
    • 3-Bucc Brass catcher attachment point


    • Tactical Innovations lower
    • Hand Selected Lower Small parts kit
    • Geissele SSA-E trigger guard
    • Ambi-Selector
    • Magpul Winter trigger guard
    • Ergo Grip with Ambi-Palm Swell
    • Magpul PRS with MDT enhanced butt plate

    Optics & Sighting systems:

    • Vortex PST 4-16x50 EBR-1 MOA (with MOA turrets)
    • PST High Rings
    • Wheeler 30mm Anti-Cant Device
    • PRI front Folding BUIS
    • MAD folding rear copy

    Thank you all for taking the time to read my post, and I look forward to any and all constructive comments you might have


    Last edited by AbHobbyist; 12-27-2017 at 09:59 PM.

  7. #7
    After Action Report - Range Report One

    Good Day all!!

    I finally made it to the indoor range last night to text my 6x45 build.

    There were two function tests that I wanted to conduct, and if I had time, I also was hoping to shoot some 5 round groups.

    A. Function Testing

    The first test was 1 round mag test:

    Put one round in a proven & reliable mag, and fire it. The purpose of this test is to see if the gun is has sufficient gas to function properly, and engage the bolt hold open function of the bolt latch assembly.

    It is possible to have enough gas to eject the case, but not enough to hold the bolt open, and its important Make sure the chamber is inspect to see if the case has been ejected.

    During this test we also want to observe the angle of ejection
    The normal angle of ejection is 2-3 O’clock (on a table marked from 12, 1,2,3,4,5,6 o’clock) If your AR is functioning fine, then it is possible to note if its on the low or high side of the normal range. Further the angle of ejection is an indicator of velocity of the BCG.
    If velocity is high, and the bolt is hitting hard, the ejection will be in the 1 o’clock area.
    If the bolt is coming back very softly, the ejection may be closer to the 5-6 o’clock angel

    The second function test I wanted to was the 5 round test.
    Here you simply put 5 rounds in a proven magazine, and see how the gum functions. This will either confirm, or disprove the 1 round function test, and give us further indication if any futher trouble shooting is required.

    All shooting was done at 50m indoors fully supported off the bench, using my #1 10 round metal LAR mag (the most reliable mag I have). I also used a brass catcher I made. The rifle was properly lubricated prior to starting testing. My set up looked as follows.

    I started with the 55 grain Nolser Ballistic Tip Reloads.

    I have tabulated the data, and the results were as follows:

    Its interesting to note that though I had proper function with the One Round test at 23.0 Grains, but did not have proper repeatable function until 25.0. At this point I felt it was to early to draw any conclusions, and thought further testing was in order.

    I next moved to the 70 Grain Sierra Blitz king reloads

    I have tabulated the data, and the results were as follows:

    Again it was interesting to note that Reliable function in the One Round test was attained at the 26.0 level, but I had full proper function in the 5 round test at the 25.5 level.

    Function test Conclusion

    The current gas port size is 0.093 and I think this is sufficient.

    Some more work with different powders and projectiles will be in order, however I think some of the function issues, as I was unable to reproduce them, are simply due to the newness for the BCG, and given some time for break in, should function with our issue.

    B. Accuracy Testing

    I did have some time to do some accuracy testing, however I will have to admit, I was not at my best as I had my focus divided between watching function, and trying for accuracy. While perhaps not optimal, the following should give an indication of the accuracy potential of the rifle.

    Again all shooting was done at 50m indoors fully supported off the bench, these are 5 shot groups. Its also worth while noting that I had 100% function, and bolt hold open function onall loads tested.

    55 grain Nosler Ballistic tip

    Test Target is as follows:

    Group sizes were mesured outside to outside, with 0.243 )caliber size subtracted. The tabulation as follows:

    Here is a shot of the fired casings.

    (please note: different load levels were identified by making the prime with different colored sharppie felt pens)

    As you can see, there is no flattening, and all primers have rounded edges and stayed with in the pocket. To my mind, there are no pressure issues here!!

    70 grain Sierra BlitzKing

    Test Target is as follows:

    Group size tabulation as follows:

    Here is a shot of the fired casings.

    (Again please note: different load levels were identified by making the prime with different colored sharppie felt pens)

    Again you can see, there is no flattening, and all primers have rounded edges and stayed with in the pocket. To my mind, there are no pressure issues here!!

    Over all conclusion

    For the first range visit I am very pleased with the results.

    I believe that the gas port is of sufficient size, and giving good fucntion.

    The initial accuracy testing shows promise, and I am looking forward to working further with this rifle.

    Well I have rambled on more than long enough.

    I thank you for making time to read my post and I look forward to any constructive comments and thoughts you might have.


    Last edited by AbHobbyist; 12-27-2017 at 10:40 PM.

  8. #8
    Wow that is awesome. Great work!
    Shootin stuff in the wild west

  9. #9

    I was sent a question, and thought I my post it here as well

    What a heck of a read!........Is this some sort of "just to see" type of project? We obviously can't shoot 'yotes with these.

    To be honest, I gave up big game hunting a long time ago. However I have been know to avidly pursue paper, steel, and the odd gopher as targets.

    I have shot the 223/5.56 Nato for a while now, and hits on steel are not particularly exciting. In fact you really have to listen for "hits" especially if there is a wind.

    I am convinced that the 6x45 (6mm-223) will hit it much harder, and be easier to hear.

    I do however have some thoughts of using the 6x45 in the field in a bolt gun. This barrel more or less fell into my lap and thought it was a great way to get acquainted with the cartridge in an affordable manner.

    I only needed to change the barrel, and was able to use the rest of my existing DMR configured AR-15.

    If things go well with this AR, I will build one on a bolt gun to take advantage of the 105 grain Amax projectile.

    In the AR you are limited to a COL 2.260 Max, (so one will max out at 85-87 grain projectiles) but it will allow me to compare the performance weight to weight of the 6mm and 224 projectiles and see if the difference is worth building a bolt gun. I hope that makes sense.

    Any how I spent some time this weekend making more brass.

    I am just waiting for my case gauge to arrive. I had the builder of the barrel use the same reamer to make me a gauge to my specs.

    I find a case gauge a key tool in ensuring that all my reloads will fit the chamber. I Hope to have some additional results to report soon.

    Any how I have rambled on long enough. Till next time

    regards and all the best

    Last edited by AbHobbyist; 12-27-2017 at 10:42 PM.

  10. #10
    Very methodical. Plus the rifle looks like a nice target setup. I do however think it deserves a true low profile gas black without the pic rail! But really that's just aesthetics. I like it. Nice target rifle.

    If I could make one minor suggestion. I would do some testing with the linear compensator off as well. It likely won't make any difference but sometimes that can be a variable, or just the weight on the end may enhance or degrade accuracy due to harmonics. Worth checking out at this stage.

    Group C with the 55 Nosler looked very promising. Just out of curiosity, what type of FPS would these be generating with these loads and that barrel?

    I look forward to seeing how it does at 100 yards.
    Last edited by Full Metal Jacket; 02-08-2017 at 05:43 PM.

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