Inside barrel treatment for gas actuated Semi auto

CalG · Sep 27, 2014

What techniques are used to refine the gas port drilling when replacing the barrel on a gas actuated autoloading rifle?

SKS etc.

edit OPPS! I should have STFFF!

http://www.practicalmachinist.com/vb/gunsmithing/deburring-gas-ports-169891/

akajun · Sep 27, 2014

I've been drilling undersized and reaming to size on my match ar barrels.

MilGunsmith · Sep 29, 2014

Same here. Drill undersize, then ream. Use a stainless steel bore brush to deburr, then shoot a few cutting rounds.

JNieman · Sep 29, 2014

I've done the same as those above - drill under, ream to size, and deburr with brushes.

I'd also shoot a couple times into the tank and thoroughly clean the barrel. I always thought that the first round or so should do a pretty good job taking away any deformities at the edge.

sticks · Sep 29, 2014

Hasn't it been said many times that whether through land or groove .. or across both, it's kind of moot once the hole is de-burred? I'm short of being convinced that accuracy or barrel life depends on it. :dunce:

There's gotta be a bunch of 'straight shooting' guns out there to prove one way or the other.

I imagine a pro gunsmith might have a Hawkeye b'scope available to see "what's what". btw, having one (10 yrs or so) has cured me of ever brushing a bore with anything but nylon bristles. What a patch won't do gets a poured lap & there's not much in between happening on my cleaning bench.

Vs pouring a slug, could you slide a pure lead one in close to bore diameter & bump it to size from both ends with brass rods? doesn't seem it's have to be too tight to contain a burr, but Wood's metal sounds like a go-to...

Disclaimer: I'm not a trained gunsmith & my trade before retiring was 'Toolmaker', tho' I can't prove I was a good one. :skep:

MilGunsmith · Sep 29, 2014

I use a Hawkeye to ensure I am centered in the groove. A lot of my work here is porting barrels for piezo-electric transducers for pressure testing. We have to put them in the groove. I have done as many as 17 ports in one barrel, all in a groove.
We did a test and AMU also tested for accuracy with hole location. We found that location, in groove or in land or half in groove, made no difference in accuracy, but did make a difference in fouling of the gas tube.

wyop · Sep 29, 2014

Same as others: Drill undersized, ream to finish size.

SteveF · Sep 30, 2014

MilGunsmith said:
............
We did a test and AMU also tested for accuracy with hole location. We found that location, in groove or in land or half in groove, made no difference in accuracy, but did make a difference in fouling of the gas tube.

Interesting. So I assume that means in the groove gave the least fouling. Correct assumption? How much of a difference, 5% or 50%?

Steve

MilGunsmith · Sep 30, 2014

Centered in the groove gave the least fouling, the worst fouling was half in the leading edge of the land.

Dave W · Oct 2, 2014

Some of the AK guys make a tool - basically some welding rod bent into "tongs" - to reach inside the barrel, find a groove, and let them mark the outside of the barrel to drill.

Fulmen · Oct 3, 2014

@ Milgunsmith: Fine, but how much difference did you find? a 1% difference isn't that big a deal, 10% might be.

As for timing the gas hole to the rifling that's not a big challenge, but how do you time this to the barrel extension threads without affecting the lengthwise position of the hole?

CalG · Oct 3, 2014

MilGunsmith said:
I use a Hawkeye to ensure I am centered in the groove. A lot of my work here is porting barrels for piezo-electric transducers for pressure testing. We have to put them in the groove. I have done as many as 17 ports in one barrel, all in a groove.
We did a test and AMU also tested for accuracy with hole location. We found that location, in groove or in land or half in groove, made no difference in accuracy, but did make a difference in fouling of the gas tube.

I've always wondered how the pressure curve went as the projectile uncovered the gas port on something like a gas charged semi-auto.
Also, have you any references to event timing with respect to when the projectile position and the motion of the action?

"It all happens so fast, I just can't seem to see what goes on when" ;-))

CalG · Oct 3, 2014

Fulmen said:
@ Milgunsmith: Fine, but how much difference did you find? a 1% difference isn't that big a deal, 10% might be.

As for timing the gas hole to the rifling that's not a big challenge, but how do you time this to the barrel extension threads without affecting the lengthwise position of the hole?

Fulman

How would such percentage measurements be calculated? Units of weight accumulated in the gas tube or barrel? i.e. mg per fired round?

At best, the variables would be confusing. "Shooting out the fouling" etc.

I bet one could go through a lot of ammo in search of that number.

Fulmen · Oct 4, 2014

CalG: Don't ask me, I'm not the one claiming to see a difference

. But I assume that if one is able to conclude that A fouls more than B, one should also be able to guesstimate the difference at least to one order of magnitude. If you can't even ballpark a number I seriously start questioning the results, saying A is better than B is in it self useless information unless A comes at no extra cost.

CalG · Oct 4, 2014

Fulmen said:
CalG: Don't ask me, I'm not the one claiming to see a difference . But I assume that if one is able to conclude that A fouls more than B, one should also be able to guesstimate the difference at least to one order of magnitude. If you can't even ballpark a number I seriously start questioning the results, saying A is better than B is in it self useless information unless A comes at no extra cost.

I agree. Subjective evaluation is sometimes all we have to work with. ;-)

MilGunsmith · Oct 10, 2014

We weighed gas tubes before and after firing to measure build up. This was done with 1000rds per bbl and 12 bbls. Gas tubes were removed before each cleaning cycle to ensure that solvent wwas not affecting gas tube. Not a short test. If I can figure out how to post a picture of the pressure curves youu can see the drops.

akajun · Oct 10, 2014

Mil gunsmith, I also, though I don't have your testing abilities to back it up. , believe that putting a gas port in a groove makes no difference in accuracy. I had a Douglas barrel chambered by frank white that seas actually centered in a land on a service rifle . that barrel was accurate as he'll, and lasted 7500 rds before it would no longer clean the 300yd stage. It still however would clean the 200.
What I have found is that a port that splits a land and groove tends to wear less as it is fired . One centered in the groove. , or a land , tends to get that little run down the barrel.
As far as a 1% change in fouling , I never noticed that, and doubt that I would. I only clean my competition rifles every 3 months or every 500 rds, and that's mostly to prevent alibis .

CalG · Oct 10, 2014

Are there "preferred treatments" for gas cylinders and pistons?

akajun said:
Mil gunsmith, I also, though I don't have your testing abilities to back it up. , believe that putting a gas port in a groove makes no difference in accuracy. I had a Douglas barrel chambered by frank white that seas actually centered in a land on a service rifle . that barrel was accurate as he'll, and lasted 7500 rds before it would no longer clean the 300yd stage. It still however would clean the 200.
What I have found is that a port that splits a land and groove tends to wear less as it is fired . One centered in the groove. , or a land , tends to get that little run down the barrel.
As far as a 1% change in fouling , I never noticed that, and doubt that I would. I only clean my competition rifles every 3 months or every 500 rds, and that's mostly to prevent alibis .

Treatments that are shown to improve free movement and operation in spite of use or neglect?

Obviously clean and "lightly lubricated for corrosion protection" is always advised. How about "silver plating" ;-) or some such?

akajun · Oct 10, 2014

I have never found a need for any special treatment on a competition rifle
. However anti corrosion platings like chrome , nickel, and melonite do have their place in guns used in harsh conditions like jungle environments or duty belts .
I can tell you though that when I chamber a new barrel that if I don't rub unicorn semien in the bore and shake a voodoo doll over it , it won't shoot worth a damn.

Inside barrel treatment for gas actuated Semi auto

Diamond

Stainless

Stainless

Titanium

Cast Iron

Stainless

Cast Iron

Titanium

Stainless

Aluminum

Cast Iron

Diamond

Diamond

Cast Iron

Diamond

Stainless

Stainless

Diamond

Stainless

Similar threads