Let's talk precision gas guns

[michaelclm]

Hopefully we end up with some good conversations about the various aspects of precision gas-operated rifles.

I will get us started:

I recently bought an LR308 with a 24" bbl.
I am trying to decide whether to have the barrel cut down and, if so, to what length.
I will be having the barrel threaded anyway so having it all done at the same time makes sense.

Now to take it a step further. Do I reprofile the barrel? Some of what I've read says the heavy "truck axle" profile is unnecessary.

Here's what I want to do with it: Medium- to long-range precision shooting (600-1000m). I can only get onto a range that exceeds 300m about once (maybe twice) a year but that trip should be a fun one, right? The majority of my practice will be on 1/4-scale targets at 300m (I'm taking suggestions here, too, by the way). My thought has been to cut the barrel to 20" and thread & maybe reprofile it at the same time.

Thoughts? Thanks, in advance.

 

[Ksmirk]

Well I'll chime in, a 20" barrel will get you to 1K seen it done several times your just gonna give up a little velocity but not a whole bunch and I would recommend 175gr SMK's. I'm gonna say it and I may be totally off base but I don't know if I would reprofile your barrel, just some issues with stresses in the metal PLUS the heavy barrels are nicer for extended range sessions as they take a bit of heat before they heat up and the accuarcy goes South.

Question though why would you want to lighten it up? the LR game is nothing fast and mostly shot from prone so you don't have to hold the rifle up and if so you'll have a sling. Another question what do you want to thread the barrel for?

Not knocking anything just asking. Later,

Kirk

 

[dennishoddy]

I'm not a precision long range shooter for the record.
I saw a pic of a 10 round group from an AR-10 that is the size of a baseball at 800 yds shot this last weekend by a guy that is a precision long range shooter.
I watched him put a smaller group than that at 600yds, so I totally believe him.

 

[michaelclm]

Well I'll chime in, a 20" barrel will get you to 1K seen it done several times your just gonna give up a little velocity but not a whole bunch and I would recommend 175gr SMK's. I'm gonna say it and I may be totally off base but I don't know if I would reprofile your barrel, just some issues with stresses in the metal PLUS the heavy barrels are nicer for extended range sessions as they take a bit of heat before they heat up and the accuarcy goes South.

Question though why would you want to lighten it up? the LR game is nothing fast and mostly shot from prone so you don't have to hold the rifle up and if so you'll have a sling. Another question what do you want to thread the barrel for?

Not knocking anything just asking. Later,

Kirk

I had read the same thing on the velocity question regarding the 20" bbl.
That makes sense about the heat.
The lightening question was primarily in regard to a couple of opinions regarding the barrel profile. You make a good point regarding shooting from the prone but there may be times where I'm shooting from uncomfortable/hasty positions if I decide to hunt with the rifle (my thought, anyway).
The rifle is going to end up a supressor host so for now I will have a thread protector installed until I decide on a can and its corresponding break/adapter.

I'm not a precision long range shooter for the record.
I saw a pic of a 10 round group from an AR-10 that is the size of a baseball at 800 yds shot this last weekend by a guy that is a precision long range shooter.
I watched him put a smaller group than that at 600yds, so I totally believe him.

His name isn't Kirk, is it?

 

[jtischauser]

I have a LR308 that has the barrel cut down to 18" and it was turned down to .750. It's a 3 gun rifle so weight was definitely an issue. I haven't shot it past 400 and I've only used the cheapest factory loads I could find so I can't give u any info on accuracy.

If you can only shoot out past 300 a couple times a year you can use a 16" barrel or whatever you want to practice at 300 can't you?

 

[michaelclm]

I can use the shorter barrel length to practice at 300m but then I sacrifice accuracy when I am able to shoot out to 600 and beyond. At some point I would like to get into long-range precision matches and I will definitely need the accuracy at that point. I will also need to strike a balance with weight under those circumstances.

Of course, I will need to stretch my practice sessions out to longer distances more frequently to gather data on my rifle and ammo under various conditions when I start getting into the LR match competition.

 

[jtischauser]

I wish Aryan would jump on here. That guy is a long range guru!

 

[Ksmirk]

I've not shot groups Dennis is talking about in a long time! best to date is 9" at 1K while not as good as some I've seen it still tickles me pink! I have a couple LR rigs and while it's not the lightest thing in the world I take my 308 along deer hunting often, actually the weight makes it nice for offhand shooting as the weight actually locks everything down. Thing about the LR game is you'll find that you will end up changing your hunting, you'll give up tree stands and you don't seem to care to get as close as you used too.

I built a 284Win just for hunting and it has a light barrel, it's good for 3 good well placed shots and well it will reach a lot further than I feel comfortable shooting! we throated the chamber to load bullets out further and in the velocity area a 7Mag I'm about equal if not a touch more BUT I've found these little deer in Oklahoma can't take that bullet very well LOL Later,

Kirk

 

[MrTheBigOx]

I can use the shorter barrel length to practice at 300m but then I sacrifice accuracy when I am able to shoot out to 600 and beyond. At some point I would like to get into long-range precision matches and I will definitely need the accuracy at that point. I will also need to strike a balance with weight under those circumstances.

Of course, I will need to stretch my practice sessions out to longer distances more frequently to gather data on my rifle and ammo under various conditions when I start getting into the LR match competition.

Since when did a short barrel become less accurite than a longer one? If its shorter it will be stiffer less harmonics so it should beore acurite.
I was told that by chopping below 20 or so inch's in a 308 you will loose around 50fps/inch. I dont use a chroney so I guess its true all I know is that shorter is louder and loud is good

 

[michaelclm]

The shorter barrel reference was in regard to a carbine- to mid-length barrel like Jesse was talking about. There are some issues that will affect accuracy past 600m with, say, a 16" barrel.

Maybe the question is better posed this way: I have a 24" heavy bbl. Do I absolutely have to have that much bbl for the ranges I'm talking about (I don't think that I do) and if not do I take it down to 22" or 20"? Why?
For the record: I am not married to the idea of reprofiling the barrel.

Will a 20" gun shooting either 168 or 175gr SMKs give me the results I'm looking for if I do my part (fundamentals) and pair the rifle with optics that are up to the task? I think that it will but that's why I'm asking: I am new to this.

 

[The Antichrome]

Where's Ben Sons when we need him?​

 

[nikatkimber]

IMO - and I'm not a guru by any means, the only benefit you get with reprofiling is lower weight. So if you are going to carry it around - hunting or comps etc - then it would probably be worth it. If you will almost always be shooting on the range from a bench, then it probably wouldn't be worth the money.

Fluting could be another option to consider rather than reprofiling, and it might be cheaper.

 

[MrTheBigOx]

The shorter barrel reference was in regard to a carbine- to mid-length barrel like Jesse was talking about. There are some issues that will affect accuracy past 600m with, say, a 16" barrel.

Maybe the question is better posed this way: I have a 24" heavy bbl. Do I absolutely have to have that much bbl for the ranges I'm talking about (I don't think that I do) and if not do I take it down to 22" or 20"? Why?
For the record: I am not married to the idea of reprofiling the barrel.

Will a 20" gun shooting either 168 or 175gr SMKs give me the results I'm looking for if I do my part (fundamentals) and pair the rifle with optics that are up to the task? I think that it will but that's why I'm asking: I am new to this.

OOOOO Knowledge

 

[JasonC]

Another option is a 6.5 creedmore gasser. I built mine for distance and speed. Here are the specs:
JD machine upper and lower with upper milled for side charge.
Magpul MIAD grip and PRS stock for AR15.
Hard chrome bolt milled down to 12.9 oz.
A2 buffer with silicon spring reduced to 6 lbs. 4 oz.
Criterion 20" stainless bbl. threaded with JEC brake.
Badger handguard milled down to 16.2 oz.
Pallidin gas block and Timney trigger.
With factory Hornady 140 AMAX this gun is a tac driver but only runs 2650 fps at 2000 density altitude.

 

[Scott Hearn]

Another LR amateur chiming in but I do have some machining experience. What Kirk is talking about is residual stress in the barrel. They all have at least a little and if it's been heated up pretty hot in the past could have more than normal (think about those guys doing the "hold my beer and watch this" mag dumps on youtube). It's possible that when turning the barrel can be chucked up and centered perfectly on the bore from end to end. Then the barrel would be turned and when finished it may not be as straight as before due to the metal on the outside holding it straight being removed. The movement is some of the stress being relieved. The reverse is also possible with the cutting tool putting stress into the barrel but if they use the right cutting tool and parameters not real likely. Hope that makes sense. A quality barrel will not have this issue because of proper heat treating, but it is possible. Probably not much to worry about.

I think the bigger issue is you deciding whether the lighter weight is of enough benefit to do it in the first place. A light weight barrel isn't inherently any less accurate than a monster heavy barrel. How many shots in a string will it take to heat it up moving POI is the real question.

 

[michaelclm]

Based on the information I've been able to acquire I think that 18" in the current profile is going to get me where I need. I appreciate the info on the reprofiling. I am looking forward to getting this thing on the range. Given the cost of everything I need I should have it range-ready by October. My rings came in the other day and I'm dropping off the upper this weekend at USSA for Dave to do his thing.

 

[aeropb]

What game were you planning on shooting?

 

[drmitchgibson]

Then the barrel would be turned and when finished it may not be as straight as before due to the metal on the outside holding it straight being removed. The movement is some of the stress being relieved.

This would only be true of a cold-worked barrel. Either cold-drawn (extremely unlikely except on black powder guns) or hammer-forged (not likely).

 

[Ben-Sons]

On a bolt gun I am a fan of a FAT heavy barrel, on a gas gun I like a heavy barrel but nothing too crazy.

There is a case to be made for a shorter barrel being more ridged, there for more accurate. That being said, I still have a couple that are 26"
I've seen 16-18" hit over 1k, so length isn't as big of an issue as people make it out to be. Less velocity means more elevation needed and the round will go trans-sonic sooner.
I'd have no issues running a 20" heavy contour (with or without flutes) all day every day.
Pick a rig, buy it, master it!