Handload problem or short barrel problem?

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DocTinker
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Handload problem or short barrel problem?

Post by DocTinker »

I wasn't sure whether to post this in handloading or the AR15 section, because I'm not sure if I have an undergassing problem because of my barrel length and gas port size, or if it's just a problem with my handloads.

Briefly: built an upper with a custom-machined 6.5" barrel. (A "Poor Man's Honey Badger.") Low-profile gas block with pistol-length gas (obviously). The gas port size was originally drilled at .0785".

I had two loads to test with: factory Remington UMC 115 gr and a subsonic handload I slapped together. The handload is Hornady brass, Winchester small rifle primers, 11.5 grains of IMR 4198 and a Speer "Hot-Cor" 200 grain hollow point. I probably should test fire with some factory subsonics, but I also handload for .458 SOCOM and so I had the IMR 4198 on hand, and the Speer bullets are really cheap on Midway.

Current problem is that the subsonics won't cycle. Gas port was originally .0785". Nothing cycled right at that size. Supersonics half-extracted, and subsonics didn't unlock the bolt. I opened the port up to .110" and the supersonics cycled fine. But now the subsonics are half-way extracting. So progress, but not a solution. I opened the gas port up to .120" and I'm still getting the same results.

Before I go bigger on the gas port, I thought I'd seek some advice.

So, does anyone know whether this load is reasonable? Should I theoretically be able to get the bolt to cycle with 11.5 grains of IMR 4198 under a 200-grain bullet? Has anyone got any load data using these cheap Speer 200-grain bullets?

Should I be opening the gas port up larger? I'd hate to put a Noveske Flaming Pig or Krink brake on this rifle, since I really don't want to go longer than the 6.5" barrel if I can help it, but if that might solve my problem, that's another option.

Ultimately, I'd like to find one inexpensive subsonic handload that works and stick with that. I have a nice load for my .458 SOCOM that uses IMR 4198 and 500 grain Hornady RNs, so I'd be happy if I could find a single load for this 300 BLK too.

Any thoughts?

Thanks,
Aaron Baker
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farm use
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Re: Handload problem or short barrel problem?

Post by farm use »

I would say its the powder. I would try A1680 or lil gun. I know you want to stick with your powder but if its not producing enuff gas to cycle them you need to move on.
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Re: Handload problem or short barrel problem?

Post by DocTinker »

farm use wrote:I would say its the powder. I would try A1680 or lil gun. I know you want to stick with your powder but if its not producing enuff gas to cycle them you need to move on.
I'm not completely married to this powder. A different powder is an easy change to make. I use this stuff for .458 SOCOM, so it's not like the rest of what I have would go to waste.

A1680 seems to be a really popular powder. But I'd like to know if that is the consensus suggestion for creating enough more gas to cycle on this 6.5" barrel?

Anyone else?
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Re: Handload problem or short barrel problem?

Post by rjacobs »

DocTinker wrote:
farm use wrote:I would say its the powder. I would try A1680 or lil gun. I know you want to stick with your powder but if its not producing enuff gas to cycle them you need to move on.
I'm not completely married to this powder. A different powder is an easy change to make. I use this stuff for .458 SOCOM, so it's not like the rest of what I have would go to waste.

A1680 seems to be a really popular powder. But I'd like to know if that is the consensus suggestion for creating enough more gas to cycle on this 6.5" barrel?

Anyone else?
A1680 is AAC's recommended powder for the subsonics.

I dont know to many people who have messed with a 6.5" barrel so I think you are in uncharted territories possibly.
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Re: Handload problem or short barrel problem?

Post by gunnyart »

I just had a good conversation with Ron from RMWXtreme. He has had great success with fast burning powders in short barrels. While A1680 is a common choice it is far from ideal. A1680 will produce a lot of gas and may help the cycling issue but I would look for a powder that will be fully consumed in your 6.5" barrel or else the muzzle pressure will significantly add to the noise. His recommendation is more often than not Lil' Gun.
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yondering
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Re: Handload problem or short barrel problem?

Post by yondering »

gunnyart wrote:I just had a good conversation with Ron from RMWXtreme. He has had great success with fast burning powders in short barrels. While A1680 is a common choice it is far from ideal. A1680 will produce a lot of gas and may help the cycling issue but I would look for a powder that will be fully consumed in your 6.5" barrel or else the muzzle pressure will significantly add to the noise. His recommendation is more often than not Lil' Gun.
Helping it cycle is the whole point of using A1680. Recommending a faster powder that produces less gas doesn't make sense for a gun that has cycling issues; that will only make it worse.

Personally I think your 6.5" barrel is a little too short, but it may work fine with a suppressor.
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Re: Handload problem or short barrel problem?

Post by Maryland_Shooter »

DocTinker wrote:I wasn't sure whether to post this in handloading or the AR15 section, because I'm not sure if I have an undergassing problem because of my barrel length and gas port size, or if it's just a problem with my handloads.

Briefly: built an upper with a custom-machined 6.5" barrel. (A "Poor Man's Honey Badger.") Low-profile gas block with pistol-length gas (obviously). The gas port size was originally drilled at .0785".

I had two loads to test with: factory Remington UMC 115 gr and a subsonic handload I slapped together. The handload is Hornady brass, Winchester small rifle primers, 11.5 grains of IMR 4198 and a Speer "Hot-Cor" 200 grain hollow point. I probably should test fire with some factory subsonics, but I also handload for .458 SOCOM and so I had the IMR 4198 on hand, and the Speer bullets are really cheap on Midway.

Current problem is that the subsonics won't cycle. Gas port was originally .0785". Nothing cycled right at that size. Supersonics half-extracted, and subsonics didn't unlock the bolt. I opened the port up to .110" and the supersonics cycled fine. But now the subsonics are half-way extracting. So progress, but not a solution. I opened the gas port up to .120" and I'm still getting the same results.

Before I go bigger on the gas port, I thought I'd seek some advice.

So, does anyone know whether this load is reasonable? Should I theoretically be able to get the bolt to cycle with 11.5 grains of IMR 4198 under a 200-grain bullet? Has anyone got any load data using these cheap Speer 200-grain bullets?

Should I be opening the gas port up larger? I'd hate to put a Noveske Flaming Pig or Krink brake on this rifle, since I really don't want to go longer than the 6.5" barrel if I can help it, but if that might solve my problem, that's another option.

Ultimately, I'd like to find one inexpensive subsonic handload that works and stick with that. I have a nice load for my .458 SOCOM that uses IMR 4198 and 500 grain Hornady RNs, so I'd be happy if I could find a single load for this 300 BLK too.

Any thoughts?

Thanks,
Aaron Baker
OK, I have lots of thoughts, and the first one I have is we haven't got enough information.

What buffer/spring combo are you running?

Now is this a rifle or a pistol?

.120 is - at least in my mind - pretty close to as large as I'd want to make the hole (.125 is as large as I'd go, then use an adjustable gas block).

My suggestion - and also what I did with a brand new upper:

Bought 20-40 rounds of factory subsonic ammo for test purposes. If you don't start at the beginning, it's just guessing.

I'd start with a standard carbine buffer and spring (assumes it's a rifle).

Drop ONE round of factory subsonic in a mag, fire. Should lock open.

Drop ONE round of supersonic in a mag, fire. Should lock open.

If it locks open, next go to 2 rounds; the goal being succesfully eject a spent round and strip the next round from the mag.

You are running a 6½ barrel, a pistol length gas system and I think you did list the load you are running.

There has to be a number - chamber pressure - for each gas system that will successfully cycle the action. I'll make an educated guess as to what that number is tonight and check your load against what a theroetical model produces.

I am thinking pistol is maybe 23K PSI, BUT that's just a guess. It could be 21.5K, or 25K, but I certainly think it's in that ballpark.

So let's just stop there and see how far you get before we venture any guesses.

Take with you an H and H2 buffer.

If one round mag test doesn't lock back on an empty mag, move to the H buffer/spring combo, observe the one round in the mag test to see what combination, if any, allows the thing to function properly.
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DocTinker
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Re: Handload problem or short barrel problem?

Post by DocTinker »

More information it is, then, Maryland Shooter.

It's a standard carbine buffer and spring in a carbine buffer tube. The current lower is my already-registered SBR lower, but I'll be swapping to its dedicated host SBR lower once the tax stamp arrives for it. It also has a standard carbine buffer and spring.

So it's a rifle, not a pistol.

I'm not inclined to go any larger than .120" on the gas port, and I don't intend to use an adjustable gas block.

I didn't start with factory subsonics, but I did start with with factory supersonics.

Factory supersonics fire, strip new rounds, and lock back on an empty mag.

It's the non-factory subsonics that are a problem, obviously. I guess I need to order some factory subsonics to be sure it's possible to cycle those.

I don't have any other buffers... what benefit would I see from a heavier buffer? It seems like that would slow down recoil, making it less likely to eject and lock back? Maybe I'm wrong...

Anyway, I appreciate the help.

Aaron
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Re: Handload problem or short barrel problem?

Post by Maryland_Shooter »

OK, to begin with, I have incomplete load data:

Is this the bullet? #2211

http://www.speer-bullets.com/products/r ... t_cor.aspx
Image

I could swear you said it was a cheap HP??? These are sold in boxes of 50, ergo casting doubt on "cheap." Also not a HP, but a SP.

I looked and didn't find any "Speer 'Hot-Cor' 200 grain hollow point" bullet, just the 2211 and a ".308, 200, Speer TBBC #1770."

What is the # on the box if you still have it?

No suppressor as well I gather from the post about muzzle devices.

OK, so using the 2211 with 11.5g of IMR4198 and a COAL of 2.12, I get 1,015 FPS with a chamber pressure of 24,450.

11.8 looks like the ceiling for subs at 1,041 FPS. Remember, it also depends on ambient air temp as well as elevation relative to sea level. That data would be helpful . . .

Again - these are theory models and theory and reality often part company when you pull the trigger. Not a big deal, just the nature of mechanical things.

However, I looked for AACs load of 11.2g of A1680, 220g SMK and came up with a velocity of WAY past subsonic at almost 1,300 FPS (vs their claimed 1,010) and a chamber pressure of 28K (vs their claimed of 21K) out of the stated 16" barrel.

I had to drop my load down to 9.3g of A1680 to get to 1,013 FPS.

Another question came to mind: you made this, so where did the BCG come from? Used in another rifle or brand new?

No matter where you got it, I ALWAYS replace the spring/extractor with the Bravo Company upgrade kit. It's like $12 for 3 of them.

http://www.bravocompanyusa.com/BCM-Extr ... 03pack.htm

As far as what another poster stated about propellant burned, Lil'Gun was 90%, 1680 about 70%, IMR4198 @ 75%, H110 @ 85% and IIRC each generated a chamber pressure exceeding 21K psi (using a 220g SMK as the projo).

So what does all this mean? There are no easy answers. You are close - if indeed it works at all - I am guessing on that as much as anyone.

Get the BCM Extractor kit, it can't hurt and wouldn't it be grand if all of this is corrected for $4?

The heavier buffer should slow down the BCG's movement. If the dwell time (time it takes the BCG to unlock, extract, move back, strike the buffer, compress the spring and then start its forward movement, stripping the next round off the mag) isn't long enough for the mag spring to push the next round into place.

So naturally this brings me to the next question - what the hell is half extracting?

The load you are using is within range. Try a new/different BCG, spring for the $12 kit.

It very well may be the hole will have to still be larger; however, you'll quickly run up against the hole in the tube itself or the gas block as a limiting factor and right off the top of my head, I don't know what size those holes are. You might check BiggerHammer.net for that dimension.

ETA: This Link

http://www.ar15barrels.com/prod/operation.shtml
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Re: Handload problem or short barrel problem?

Post by emerson »

The simple fix is to switch powders.

1680 will likely solve your problem.
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