Where can I find a gas block with a .071 port?

[kimbercollector]

7.5 inch AR / SBR

Bolt fires and loads a new round before the spent casing can be ejected. Creates a stovepipe every 2-3 rounds.

This is looking like a over gas issue...right? Pushing my bolt back too fast?

I called Troy. Im using their M7A1 stock. They say they felt a .071 gas port is best for this new stock system. They said the buffer is as heavy as its gonna get.

So where can I find this gas block? Do adjustables work well here?

Many thanks...

 

[phylodog]

An adjustable gas block may be easier to locate. I've not seen gas blocks listed by port size, doesn't mean they're not out there.

 

[Squirt239]

http://www.brownells.com/rifle-part...ar-15-m16-adjustable-gas-block-prod55124.aspx

 

[wsenefeld]

This could be a plethora of things so don't think a gas block is going to solve your problem.

You aren't correctly understanding what Troy was trying to convey. They said a 0.071" gas port was ideal. The gas port is the hole drilled into the barrel. The gas block is an entirely separate part. Purchasing a gas block is not going to solve your gas port issue (if that's even the case).

Instead of calling Troy (the maker of your stock), you should call whoever manufactured your barrel and ask them how large the gas port is. If they say something near 0.071", they must have done their homework. In the mean time, disassemble the upper and put a set of calipers to it and measure the gas port yourself. If the gas port is between 0.068-0.075 you'll be fine.

Troy suggesting a 0.071" gas port is also specific to your 7.5" barrel. Not a general assumption to be made for anyone using the m7a1 stock. Different barrel length/gas system length combos need different gas port sizes.

This could also be a tight or improperly finished chamber which causes it to hold on to the brass.

If your bolt carrier group is going to fast and it's letting go of the case, you have a weak extractor spring that's just freely lipping over.

If your bolt carrier group is going too fast and it's ripping the rim off of the case, then your extractor spring isn't weak and the bcg simply needs to slow down.

Your bcg could also be going too slow which allows the brass to expand too much inside the chamber before being extracted. Again though, if your brass looks fine, you have a weak extractor spring. In the case of a slow bcg and a strong extractor spring, the rim would not be ripped off. Instead, the bcg would simply be unable to unlock from battery without a good "mortaring".

I'm guessing this is a franken gun that you built yourself? Possibly even your first build? Anyways, good luck in your gas block search.

 

[kimbercollector]

Spikes factory 7.5, no frankengun, but that M7A1 is def different bolt and buffer combo, with a seemingly super light tensioned spring...

I tried a separate RRA Bolt, its bolt face was a bit more deep than the Troy. Had a 'sharper' extractor too. No love, same prob.

Did the old, IPhone slow motion video next to it...fun to watch. Brass case rim shows no damage.

Thanks for all the info...Gonna start with a barrel port caliper measurement...

At least its just a fun gun, never a carry gun but still want to get confidence up with it/working out the issue.

 

[upchurch67]

This doesn't sound like an overgas issue to me. I think one thing wsenefeld was trying to say is that if there is not damage to the case and it's still in the chamber, then your extractor doesn't have enough tension or maybe is damaged. I would spend the $15 to try a buffer technologies extractor upgrade. I was having an occassional failure to extract until I installed one of these.