Question: drilled gas port and low/high power ammuntion

[Dosssch]

Greetings from Sweden

Like everyone else, I have had problems firing low power 7.62 ammunition in my M&P10 Sport.

I recently drilled up the gas port with a 2mm drill (0.078 ").
I have also changed my gas block to an Odin adjustable gas block.

My question is if I will destroy the barrel or gas block if I tune my gas block to shoot low power 7.62 ammunition and then fire high power 308 180 grain Sierra GameKing ammunition?


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[WR Moore]

Please define "high power" and "low power". I vaguely recall some really low pressure/velocity/light bullet gallery ammunition used at one time by the Bundeswehr that I expect required manual operation of the bolt on the G1 and G3. If you're just referring to bullet weight, I'm not terribly familiar with the AR10/M&P10. A better way to take care of your functioning issue might have been a lighter/shorter recoil spring and/or a lighter buffer (if available). You'd have to change them to shoot the different types of ammunition but it'd been a much less of a potential problem.

Now, if you have your gas system set to function the rifle when using low pressure ammunition and then shoot high pressure ammunition without changing the gas adjustment you won't harm your barrel (except for possible excessive wear/cracks on the barrel extension locking lugs, but that may be available as a separate part). You will however, probably (rather depends upon the difference in chamber pressures) severely batter your bolt/bolt carrier/buffer due to higher than design specification bolt carrier velocity. The bolt will also be unlocking earlier at higher than than design spec chamber pressures and this will increase wear on the cam pin and bolt/bolt carrier. Expect cracked bolt body/locking lugs. We see those bolt problems on extensively used AR15 pattern rifles with standard ammunition in heavy use.

Hopefully, Odin included instructions on how to properly adjust the gas system. Writing down the adjustments (from fully closed) for both loads would be a good idea. Change adjustments as required.

 

[Dosssch]

Thanks for the advice. It sounds healthy to set the gas block to two diffent settings. 7.62 or 308.

7.62x51 NATO are made for M1 Garand and use a lower pressure (50,000 psi). While the 308Win has a higher pressure (62,000 psi).

 

[sgtsandman]

Mine has run both 7.62X51mm NATO and .308 Winchester just fine.


As far as your question, you may need to adjust the block for higher pressure ammunition when you go to shoot it. The easiest way to see if the gun is over gassed or not is to pay attention to the ejection pattern of the ejected brass.

 

[BillyMagg]

Specific issue with 7.62?

Greetings from Sweden

Like everyone else, I have had problems firing low power 7.62 ammunition in my M&P10 Sport.

I recently drilled up the gas port with a 2mm drill (0.078 ").
I have also changed my gas block to an Odin adjustable gas block.

My question is if I will destroy the barrel or gas block if I tune my gas block to shoot low power 7.62 ammunition and then fire high power 308 180 grain Sierra GameKing ammunition?


Picture:

turn picture into high resolution

I just saw this post again after seeing your input in the Radian Raptor charging handle thread..

So back to undergassed 7.62 ammo, drilling up is the right decision, a gas rifle will not function without sufficient gas..

I bought a Wilson Combat, and it also proved problematic with 7.62 X 51 with very poor ejection, the rifle ran fine, and the empties leave the rifle, but just kind of "bounced out"..

your concern is being over gassed, its very simple, you need an adjustable gas block, open it up for 7.62 X 51, turn it in a couple of turns to decrease the diameter of the metering valve with full power heavy bullet .308 ammo..

I ended up with a KAK 5.4 oz 2.5" carbine buffer and heavy orange Sprinco spring in mine, and replaced the ejector and spring with a KAK ejector and spring to addres the lethargic ejection.. the heavy buffer and spring, slow down the unlocking, and slow the recoil cycle,, a heavy buffer does indeed increase reliability, and that heavy spring and buffer assure more positive chambering of the next round off the top of the magazine..

I ended up at .995 with the heavy buffer and spring requiring more gas, I am running my gas block wide open, with the new KAK ejector, it does indeed get them out of rifle with a bit more energy... 7.62 is still not what I would like, but it is a lot more energetic. No signs of being over gassed, in fact I wish I had opened up the gas port a little more, as my gas block is wide open, as evidenced by the adjustment bolt being about 1/2 way out of the gas block..

to be clear, my rifle functioned reliably at .082, but the ejection was very poor...

what issues were you having prior to drilling your port??

and to answer your question about hurting your rifle??? it probably is just fine as is, but if you notice signs of it being overgassed, for example slamming of the BCG into the buffer stop, (yes you will feel it), that can be addressed with a heavy buffer, (Eugene Stoner designed the AR-10 to run with a 5.4 oz buffer), or a heavier spring..

what were your specific issues with the 7.62 X 51 ammo??

 

[Dosssch]

Thanks for your reply

The biggest problem with shooting 7.62 was the FTE, which means the weapon was undergassed.

It managed the standard 308 without any problems.

With a drilled pipe, it shoots everything. I'm super happy with it =)

 

[BillyMagg]

Thanks for your reply

The biggest problem with shooting 7.62 was the FTE, which means the weapon was undergassed.

It managed the standard 308 without any problems.

With a drilled pipe, it shoots everything. I'm super happy with it =)

Good for you, I'm very happy to hear she's running as she should!