6 PPC in an AR 15

J

jlcprec

New member
I have a Colt H-bar that I never shoot. I also have lots of 6mm barrels. Does anyone have any tips or experience in fitting a barrel? Can I just get the 7.62 by 39 bolt, new barrel extension, and a gas block, and have at it? Do you drill the gas port the same diameter, or should I make the gas system adjustable? Will the PPC feed with a Grendal magazine? How does a tight neck work with an AR? (I want to use my old brass, I'll use a bigger reamer) Anything else I'm missing? Anyone try to shoot a PPC with the same loads we use in a bolt gun? I'd be surprised if the AR could take that!

Jim
 
jlcprec said:
I have a Colt H-bar that I never shoot. I also have lots of 6mm barrels. Does anyone have any tips or experience in fitting a barrel? Can I just get the 7.62 by 39 bolt, new barrel extension, and a gas block, and have at it? Yes. You may want to slightly open and polish the feed ramps on the extension. Do you drill the gas port the same diameter, or should I make the gas system adjustable? Size will be somewhat contingent on location(tube length), powder burn rate, and pressure. Making the hole a tad big and using an adjustable gas block works, but keeping it as small as possible has obvious benefits. Will the PPC feed with a Grendal magazine? Yes, but you may have to tweak the feed lips on the mags slightly, as is always the case. How does a tight neck work with an AR? (I want to use my old brass, I'll use a bigger reamer) For absolute reliability, I'd spec the reamer about a half thou bigger in all dimensions. You could simply polish the chamber out a bit and use your existing reamer and dies and accomplish the same thing. It's not really any different than our bolt guns...it's all about the relationship between the chamber and die. Just make sure the die sizes the brass enough. Anything else I'm missing? Anyone try to shoot a PPC with the same loads we use in a bolt gun? I'd be surprised if the AR could take that! Max pressures in an AR15 are in the 50K PSI range. The bolt lugs on either side of the extractor are the weakest link.

Jim
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Hope this helps, Jim!--Mike

Another thing...the thin necks on your match brass will take a beating in a gas gun.
 
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There are a couple of 6mm cartridges specifically designed for use in the AR15 platform that are based on the 6.5 Grendel ctdg - 6mmAR (and the improved Turbo version) and 6 RAT. The Grendel has the same casehead dia as the PPC, and the brass that Alexander Arms sells is made for them by Lapua. The RAT was designed with across the course highpower match shooting in mind, and has ample case capacity to push 105gr bullets to 2800+fps out of 26"-28" match rifle barrels. I've owned & shot one of the 28" barreled uppers, and had very good results with it in competition. Also build myself a 24" bbl'd 6 RAT, and enjoy shooting the little 6mm AR. The RAT is fireformed by simply necking down a 6.5 Grendel case, leaving a false shoulder just above the neck/shoulder junction, very much like fireforming 6 Dasher from 6BR brass. In fact, the RAT looks very much like a Dasher, but with smaller body dia., and slightly shorter neck.

Downside to using a cartridge with the Grendel's .439" casehead dia. is that it leaves minimal amounts of steel supporting the locking lugs on an AR15 bolt. There have been reports of breaking lugs when the RAT is loaded too hot, or when bolts of less than top quality are used. Lewis Machine & Tool makes an enhanced Grendel bolt that's highly recommended. It's pricey, at $155 for just the bolt (bolt carrier not included), but I've never had a problem with the two of these bolts I've used on my own uppers, and would recommend them. Les Baer also sells a bolt for his own version of 6mm ctdg based on the Grendel case. I would not recommend using any other bolts for these cartridges. PTG made my 6 RAT reamer; Hornady makes dies, but I'm not sure who's selling them right now.
 
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jlcprec said:
I have a Colt H-bar that I never shoot. I also have lots of 6mm barrels. Does anyone have any tips or experience in fitting a barrel? Can I just get the 7.62 by 39 bolt, new barrel extension, and a gas block, and have at it? Do you drill the gas port the same diameter, or should I make the gas system adjustable? Will the PPC feed with a Grendal magazine? How does a tight neck work with an AR? (I want to use my old brass, I'll use a bigger reamer) Anything else I'm missing? Anyone try to shoot a PPC with the same loads we use in a bolt gun? I'd be surprised if the AR could take that! Jim
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The inherent accuracy of the 6PPC cartridge is completely lost, once you place it in a magazine, because you'll never be able to tune it to it's maximum capability. Finding the load is one thing, tuning it is another.

Seating depth is eliminated by the requirement that it fit inside the magazine. .001" difference in seating depth can make a world of difference when trying to put a bullet through the same hole, shot after shot, which is what the 6PPC is capable of.
 
abintx said:
The inherent accuracy of the 6PPC cartridge is completely lost, once you place it in a magazine, because you'll never be able to tune it to it's maximum capability. Finding the load is one thing, tuning it is another.

Seating depth is eliminated by the requirement that it fit inside the magazine. .001" difference in seating depth can make a world of difference when trying to put a bullet through the same hole, shot after shot, which is what the 6PPC is capable of.
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I disagree completely, and I've built some magazine rifles, tunable repeaters.

The magazine has no effect on seating depth except that on some heavy recoilers I add shoulder strips in the mag to keep recoil from changing oal of unfired rounds..

:)

al
 
" Max pressures in an AR15 are in the 50K PSI range. The bolt lugs on either side of the extractor are the weakest link. "

saami spec for 223 rem is 55000 psi cup...223 would typically be seen in a target or varmit ar rifle.

5.56 nato is 62kpsi....................5.56 is typically found in 20" rifles and in 16" CARBINES.....

this is an area of great discussion most with little facts.

gun digest did a nice artical on the subject....

most commercial 5.56 ammo sold in the usa is loaded to 223rem specs.....

why the owner of a target ot varmit rifle would shoot milsurplus 5.56 ammo in thier rifles is beyond me.....but yes there is a SMALL possibility of a less than desired results of doing so.
both rifles have a saaftey margin of 30%....................so normal ammo is not an issue..but there is a rare situtation where the throat can cause a pressure spike.....

mike in co
 
alinwa said:
I disagree completely, and I've built some magazine rifles, tunable repeaters.

The magazine has no effect on seating depth except that on some heavy recoilers I add shoulder strips in the mag to keep recoil from changing oal of unfired rounds..

:)

al
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How many in 6PPC? How many Zero and Teen groups were produced? How many grains of N-133 produced your best load? How much neck tension? How far into the lands produced the best tune? Which brass, primers, custom bullets? Tell us more about your experience with the magazine built 6PPC.
 
mike in co said:
" Max pressures in an AR15 are in the 50K PSI range. The bolt lugs on either side of the extractor are the weakest link. "

saami spec for 223 rem is 55000 psi cup...223 would typically be seen in a target or varmit ar rifle.

5.56 nato is 62kpsi....................5.56 is typically found in 20" rifles and in 16" CARBINES.....

this is an area of great discussion most with little facts.

gun digest did a nice artical on the subject....

most commercial 5.56 ammo sold in the usa is loaded to 223rem specs.....

why the owner of a target ot varmit rifle would shoot milsurplus 5.56 ammo in thier rifles is beyond me.....but yes there is a SMALL possibility of a less than desired results of doing so.
both rifles have a saaftey margin of 30%....................so normal ammo is not an issue..but there is a rare situtation where the throat can cause a pressure spike.....

mike in co
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Allow me to clarify...I should have stated that max pressures in an AR15 are in the 50K PSI range with an Alexander Arms Grendel bolt, since that's relative to Jim's post and 223/5.56 isn't.. That info came from Bill Alexander. He actually claims his bolts to be stronger than standard 7.62x39 bolts. The bolt face is .011" deeper on his Grendel bolt than the std. x39 bolts, FWIW.

As to the lugs on either side of the extractor being the weak link...I didn't do any empirical testing, just loaded till something broke while having A Pressure Trace hooked to the gun. I won't say at what pressures the PT read when the bolt failed....guess what....it failed at one of the lugs on either side of the extractor. Also, I've seen it happen more than once on .223/5.56 bolts. In their case, fatigue could be argued as a contributing factor, but not so on the AA Grendel bolt I referred to, as it was new. It could also be argued that powder burn rate and gas system length/ port size(as mentioned in my previous post) could be a contributing factor, but it happened using a gas system that was long for the powder being used(fast), and an adjustable gas block. With that setup, the gun had just started to cycle reliably when the bolt broke...so it wasn't from too much gas...Just an FYI from real world testing.
 
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You might look at TNW's long-stroke piston system as well. With a long stroke piston, an adjustable gas port, & experimenting with different weight buffers, you can probably greatly slow down the bolt carrier velocity. You could also tap the gas even further out than the piston designers intended for longer dwell time, & run a pig tail to the piston body. Downside to most piston systems is they lock to the bbl, lessening the advantages of a free-floated bbl.

http://www.whiz.to/~tnwfire/proddetail.php?prod=GPS
 
Mike, When I did the 24" bbl. for my AR15 6 RAT, I determined the gas port dia. by starting with a #48 drill, then working my way up in hole/port size by test-firing with a single round loaded in a magazine. Kept on going one number-size drill larger each time until the bolt locked back. I went with a std rifle length gas system, and was loading test ammo with IMR8208 & H87BTHPs for around 2750fps. At the time, I'd figured that 8208 would be the fastest powder I'd typically use, but since then, I've loaded H322 for fireforming ammo using Sierra 85 BTHPs, and got good accuracy, plus more sharp shouldered, fully formed cases than I was getting with 8208 & the 87s. As mentioned, I've been very satisfied with the LMT enhanced 6.5 Grendel bolt, and would not recommend using Colt's or anyone else's 7.62x39 bolts.
 
flatlander said:
Mike, When I did the 24" bbl. for my AR15 6 RAT, I determined the gas port dia. by starting with a #48 drill, then working my way up in hole/port size by test-firing with a single round loaded in a magazine. Kept on going one number-size drill larger each time until the bolt locked back. I went with a std rifle length gas system, and was loading test ammo with IMR8208 & H87BTHPs for around 2750fps. At the time, I'd figured that 8208 would be the fastest powder I'd typically use, but since then, I've loaded H322 for fireforming ammo using Sierra 85 BTHPs, and got good accuracy, plus more sharp shouldered, fully formed cases than I was getting with 8208 & the 87s. As mentioned, I've been very satisfied with the LMT enhanced 6.5 Grendel bolt, and would not recommend using Colt's or anyone else's 7.62x39 bolts.
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I really don't see a problem as long as pressures are kept within the bolts acceptable range, but I've heard lots of good things about the LMT. Is that the one that requires a different barrel extension? At some point, I remember seeing one somewhere that had a radius on both sides of each lug and a barrel extension to match, instead of the fairly square junction where the lugs meet the bolt body. I just remember looking at it online and thinking that it looked like a good answer to the problem of lugs breaking. I don't know or recall what they were made of, but would think S-7 in the mid 40'sR would be tough stuff to beat.
 
( i am pretty sure you know more and have done more with the ar platforms than i have..so i was kind of suprised at the number....)
mike in co
mwezell said:
Allow me to clarify...I should have stated that max pressures in an AR15 are in the 50K PSI range with an Alexander Arms Grendel bolt, since that's relative to Jim's post and 223/5.56 isn't.. That info came from Bill Alexander. He actually claims his bolts to be stronger than standard 7.62x39 bolts. The bolt face is .011" deeper on his Grendel bolt than the std. x39 bolts, FWIW.

As to the lugs on either side of the extractor being the weak link...I didn't do any empirical testing, just loaded till something broke while having A Pressure Trace hooked to the gun. I won't say at what pressures the PT read when the bolt failed....guess what....it failed at one of the lugs on either side of the extractor. Also, I've seen it happen more than once on .223/5.56 bolts. In their case, fatigue could be argued as a contributing factor, but not so on the AA Grendel bolt I referred to, as it was new. It could also be argued that powder burn rate and gas system length/ port size(as mentioned in my previous post) could be a contributing factor, but it happened using a gas system that was long for the powder being used(fast), and an adjustable gas block. With that setup, the gun had just started to cycle reliably when the bolt broke...so it wasn't from too much gas...Just an FYI from real world testing.
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Now my next thought is, why not just get a 6mm/.223 reamer, and avoid the feeding issues? I can use the same bolt and magazines that I already have. What are the issues with this cartridge? I know it won't be as accurate as a PPC, but I have plenty of PPC's if I really want to try and put the bullets into the same hole. If I could make an honest 1/2 to 3/4 inch rifle with a 16x scope off a rest at 100 yards, I would be very pleased.

JIm
 
The LMT 6.5 enhanced bolt does not require a special bbl extension. But most of us have made a habit of using M4 uppers & bbl extensions to enhance feeding reliability with any of the 6-6.5mm cartridges, or for that matter any cartridge with a body dia. larger than the 223/5.56. Though the extended feed ramps of the M4 design were originally intended to improve feeding in the M4 carbine (probably due to its violent cycling caused by the CAR-length gas system), they also work well with cartridges of larger dia. Use of a M4 upper with a std. bbl extension will likely cause feeding issues, since the M4 receiver's feed ramps extend just a bit below the bbl extension, and the std bbl extension's ramps don't extend down to match with the M4 receiver's integral ramps. They're not very large, but probably just large enough to capture the point of a bullet and cause stoppages.
 
As far as going with a 6x45 instead of a Grendel-based wildcat, my question would be simply "why bother?". No matter what the theoretical accuracy of a 6PPC is in an AR platform, it's not that easy to build a 6mm AR that'll beat the accuracy of a 223 AR with a good custom barrel with a good chamber. So if a particular 6mm AR cartridge offers no real improvement in ballistics over the parent 223, again, I'd ask "why bother?".
 
B/c he has a lot of 6mm bbls. Of course, he could build a 6mm/.458" SOCOM wildcat, or a 6mm/.30" Remington AR wildcat as well. My suggestion would be to stick w/ 6mm PPC, it's been run in ARs for 20 years now, & the upper & mags can then be sold as a working 6mm PPC upper when he tires of it.
 
mike in co said:
( i am pretty sure you know more and have done more with the ar platforms than i have..so i was kind of suprised at the number....)
mike in co
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The max psi is so low due to the increased bolt thrust generated by the larger diameter case of the Grendel/PPC vs. .223. Calculated bolt thrust is very comparable between the ppc/grendel@50K psi vs. .223@62K psi
The formula for thrust is psi x area.
 
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abintx said:
How many in 6PPC? How many Zero and Teen groups were produced? How many grains of N-133 produced your best load? How much neck tension? How far into the lands produced the best tune? Which brass, primers, custom bullets? Tell us more about your experience with the magazine built 6PPC.
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LOL!!

Ohhh if only it were that easy ab, :)
if only the world were small,
and black and white!

al
 
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