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Mark Hartig

Transitional Bushmaster .308 group trouble

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Hello gents

I recently acquired a Bushmaster AR-10 (?) manufactured at the time when Bushy was being absorbed by Remington. It's not clear whom the components were manufactured by and it's also not clear who assembled it. It has a 16" 1-10 twist barrel and a non floated forend with a delta ring. The rifle was new in the box at purchase.

I mounted a Trijicon 2-10x56 optic with a 30 mm tube, cleaned the oil and scrunge out of the bore, and went to the range with a few hundred rounds of Magtech 149 grain FMJ's. I followed proper barrel break in procedures and got very poor groups at 100 yards even after 60 rounds of the Magtech fired. I tried handloading for it, 40 grains of IMR-4895 behind a Sierra 165 grain HPBT and got at best a measured eight inch group at the same distance.

Having checked the optic mounting for torque, and having proven the optic itself on other platforms I can only conclude that there is something badly wrong with the rifle itself. From what I've read here the things I should be looking at are an upper receiver lap  and bedding the barrel extension. Barrel nut torque may also be an issue altho I have not yet checked it. If anyone's got additional suggestions or a better process than the one I've stated above I'd be grateful to hear about it since in it's present state the rifle is pretty much useless.

 

Regards,

Mark

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Hope you get it figured out, let us know what you find, 8 inches at 100 does indeed suck. also welcome to the site, I;m sure there will be others to offer suggestions soon.

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Thanks for the input guys I'll start at the barrel nut. Not right away tho, looks like I'll be waiting a couple of weeks for an upper vise block unless I get creative and make my own. This may happen if I get tired of waiting on the local sporting goods store

 

Regards,

Mark

 

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So the tale continues. It seems this is a Bushmaster ORC which has the Bushy logo on the lower but right next to it it sez Illion, NY so this settles the source question. After the initial debacle I took it apart, scrubbed it, and re assembled it with the addition of a Geissle (sp?) replacement trigger. Loaded more of the Sierra 165's this time with 40.2 grains of IMR-4895. Went back to the range at 100 yards and this is what it did; first pic is from the first session where it's not hard to figure out my distress, second pic done this morning. When I saw this you could've knocked me over with a fart I have no idea what happened here. I am happy, however, that it looks like I don't need to do all the things I was thinking of and now I almost don't want to clean it. Guess this barrel really hates 150 grain bullets.

 

The rifle does have a sharp, nasty recoil to it and it's trying to tear the rims off my brass on ejection. I'd put on an adjustable gas block but I'd like to retain the front sight so the fix is probably a heavier spring and buffer. Any suggestions as to weight specs?

 

Regards,

Mark

 

 

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Hey Mark   Yeppers barrels don't like certain loads/bullets and really like others....glad you found out on your own. Get the recoil down and don't over clean your barrel....leave it be for a while    :banana:   Wash

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Here’s a nice chart from Slash at Heavybuffers.com. I like his products and support small American business but if you chose to go cheaper the size and weights are relevant 

8EF46CA2-D1B6-4558-B66D-1C734DC5BCF0.jpeg

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7 hours ago, Mark Hartig said:

The rifle does have a sharp, nasty recoil to it and it's trying to tear the rims off my brass on ejection. I'd put on an adjustable gas block but I'd like to retain the front sight so the fix is probably a heavier spring and buffer. Any suggestions as to weight specs?

Good job sorting out the ammo dilemna on it. We could go hours on recoil systems, but the fix is $55 and simple.  I've written about this at length, so here's some of that info - read up, just hope back in here with questions, just to keep it all in here on your gun, and we'll sort this out quickly...  

 

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Thanks for the advice and information gents much of this I did not know. Based on what I've been able to glean from said info I now have a KAK industries 5.3 oz heavy buffer and a JP Enterprises extra power large frame carbine buffer spring on the way from Primary Arms. Between the two of them I should be able to solve the too energetic cycling problem. 

Like most of us probably I have assembled lowers before, not much to that, easier that assembling a plastic model. I have never fooled around with an upper tho, I always felt there was something off with the assumption you can just order a pile of parts and screw them together into a smooth and repeatable upper. I may try this someday but not right at the moment.

I will report results when replacement parts are installed and tested, thanks again

Regards,

Mark

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I've got a DPMS LR308-T (basically, your rifle, but with a fixed buttstock and railed gas block), and it was a beast when it came to recoil. Carbine-length gas systems on .308s with light buffers are a b!tch. I swapped in a heavy buffer and ArmaLite spring from Slash, and added a good muzzle brake, and it tamed her right on down.

I've since added an SLR adjustable gas block, but haven't had an opportunity to get out to the range and adjust it. I suspect I'll be going back to the OEM buffer and spring once I've adjusted the block -- the heavier buffer system slowed the rifle's cycling speed noticeably and, for some reason, that bothers me.

If you're still interested in an adjustable gas block, JP does make an adjustable FSB.

https://jprifles.com/buy.php?item=JPGS-2FS

Edited by COBrien

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Thanks COBrien for the link

Parts arrived yesterday and range test this morning. The fix was successful as the rifle's no longer tearing up brass and recoil's more like being shoved than punched like a well behaved gas gun should be. Don't know if I'll bother with an adjustable gas block now since the objective's been achieved. 

Thanks to all who took the time to respond to this with your wisdom to get this sorted out

Regards,

Mark

 

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