Home Forums Hunting & Shooting AR and Tactical Rifles 10.5" AR-15 5.56 Pistol

That looks good, MM.

I put mine together this afternoon and fired a test round with 24grs of Lever and a 75 BTHP. I was thinking the same about the Magnetospeed and remembered having a DPMS Levang compensator, it's not optimum but works. That load was running about 2580 our of a 16" earlier this morning at 49 degrees, 2260 out of the little booger.

I would not have expected 53 fps per inch but that is what it is for the single shot.

That's good to know.

Well, I can see when you get closer to the chamber, there would be more loss per inch, since the barrel pressure is a lot higher between 10-16" than say 16-20 inches.

Here is a comprehensive velocity test of many 5.56/223 commercial ammo types, in 10.5, 11.5, 12.5, and 14.5 barrels.

It is a little bit of a nut-roll to go through, but the links at the end of the first post have the 10.5" velocity data.

https://www.ar15.com/forums/AR-15/S...-11-5-12-5-and-14-5-ALL-DONE-/16-714088/

The Black Hills 77gr TMK and the IMI 77gr both break 2400 fps in the 10.5".


The IMI stuff in 55gr, 62gr, and 77gr is all pretty snorty compared to the others.

Thanks for the links, I am shooting for 2650-2700 fps in my 16" barrels and whatever I get in the 10.5" with 75's.

I was able to shoot one five shot group at a 100 yrds after bore-sighting that was about 1.5" and then jammed that booger up tight. One live round ended up stuck between the top of the bolt and the frame.

I had 40 rounds each running 24-25.5 grs of Lever and 75 gr BTHP's for testing in all three and to have some fun shooting. SS 10X's mounted on both and probably didn't shoot one five shot group better than 1.5", most 2"-4". One a Faxon Pencil and the other a BHW mid-weight but I don't remember the name of the profile.

I am close to parting out four and keeping the LE6920 that is completely stock and the PSA pistol.

That may indicate your rifle is severely overgassed with that load, as I've mentioned in the other thread. Weird stuff like that starts happening when the action is violently overgassed.

~23.5gr of Benchmark will get you to the velocity you want in your 16" guns, with a lot less gas and blast, and is right at a good accuracy node for 16" ARs. Save that Lever powder for the bolt guns, it's just mis-matched in the ARs.

I played around with JBM to work out a decent zero for M855 in the 10.5" barrel, at MV of 2570 fps.

Came out to a 40/200 zero in local atmo. That's what I put on the irons.

Here's what it looks like on paper.

I've been using an H3 buffer, no cycling issues with any of the commercial or handloads so far.

Cool, I have a few pounds of Benchmark but never used it with 75's so I will give it a run.

I checked PSA and neither the pistol kit or the Shockwave kit indicated what buffer is used other than "carbine" so I weighed it at 2.9 oz.

If it's overgassed from the start, why would PSA sell the kits with a 3.0 oz buffer?


If this information is correct start with an H3?

Car std 3.0oz
Car H 3.8oz
Car H2 4.6oz
Car H3 5.4oz
RRA 9mm 5.6oz


And on that same subject, what is the recommended buffer tube for a 16" barrel?

I don't know what I have now and can't get to the safe before heading out for the daily grind but I will weigh them this afternoon.

If it's overgassed from the start, why would PSA sell the kits with a 3.0 oz buffer?

They think most people will use underpowered ammo and won't shoot it much anyway. Or they just don't care.

I believe PSA err's on the large size for their gas ports.

Probably something to do with the amount of steel cased ammo folks shoot through them, it is a bit softer on performance, probably less port pressure with that stuff.

As far as buffer tubes for 16", I have used carbine and rifle recoil systems and never had issues with either. I think either is fine.

Because 99% of buyers are going to shoot the cheapest crapiest ammo made. It’ll be underpowered and cause issues if the barrel has the correct gas port size. There are almost no 10.5’s (all the way to 14.5”, and even then they tend to be over gassed for 5.56) uppers/barrels made for the above reason.

Start with an H2 buffer in pretty much every 14.5” and under.

Is an adjustable gas block a reliable solution to overgassing or would you recommend changing the buffer weight only? I have a Faxon 11.5" barrels with midlength gas. Thanks.

I'd imagine you could approach it either way.

I haven't used an adjustable gas block myself, but it would seem to give great latitude in adjustment.

I have a 14.7" mid-gas that was/is seriously overgassed, to the point the extractor was jumping the case rims. I added the o-ring under the extractor, and an H3 buffer, that settled it right down.

I was referring specifically to the Leverevolution load that RDW was shooting, not anything else. Lever works well for bolt guns in 223, but produces a lot more gas than typical 5.56 loads and as a result, it's a poor choice for an AR unless you tune the gas specifically for that load. Even if your rifle is gassed correctly for commercial 5.56 loads, it'll be overgassed for full charges of Leverevolution.

I do have one load I use it for in a Grendel, but have to open up the Bootleg adjustable carrier one notch to compensate for the gas when using that load.

Adjusting the gas is a better tuning solution, but changing a buffer is easier for most people.

Some guys are concerned about adjustment screws coming loose in adjustable gas blocks, but there are ways around that too.

Thanks. I've got my eye on a Superlative Arms gas block.

Either way is fine except if you are going to use a silencer. Then the adjustable gas block is preferred.

Gents, professing my ignorance, I have a dpms brand AR and want to do the conversion to what MM has here. You guys have covered well the sources to do that but what I need to know is what does it take to do this and remain “legal “ in the conversion from the existing 16” bbl to the 10.5” bbl ? DeFlave well advised that you cannot just simply cut the barrel down.

Any and all guidance and advice would be very much appreciated to get this right and legal from the start.

Thanks in advance, Gents.

OT