Squeezing the most accuracy out of my gas gun loads

[SWThomas]

Hey everyone! This is my first post and I hope to learn a lot here.

I have a GA Precision GAP-10 chambered in .308WIN. It has an 18" barrel, Noveske Switch-Block, and a Vortex Viper PST 4-16X50 FFP scope with the MRAD reticle. I'm in the process of working up some handloads for it and want to optimize the accuracy as much as possible. Here's a list of the equipment I'll be using in this process:

Press: Dillon 550B reloading press.
Dies: Dillon sizer, Forster Ultra Micrometer seater, Dillon crimp (if needed)
Brass: Lapua
Bullets: SMK 175g BTHP and Hornady 168g A-Max
Primers: CCI #34
Powder: Varget, IMR 4064, IMR 8208XBR
Case Trimmer: Wilson Stainless Micrometer
Misc Tools: PP reamer, flash hole reamer, Sinclair Concentricity Tool, Sinclair Comparator body with 30 cal comparator and .308 bump gauge, Lee Ergo-Prime.

My plan is to load up some of the Lapua brass and go blast it to fire-form the cases. Then I will measure the shoulder and set up the Dillon die to bump it back .003. Trim to 2.005. I'm going to seat the bullets to mag length for now. I'll run these throught the concentricity tool for each step to see if one particular step is introducing run out and try to adjust it. I don't plan to crimp right now.

I plan on conducting a ladder test at 200-300 yards going from min-max charge in 0.5g increments. Once I find my nodes I'll whiddle it down from there. Once I find "the load," I'll start playing with seating depth to see if it makes any difference.

Is there anything you see in my plans that you would change/critique? Any advice?

 

[Turbulent Turtle]

I use a gas gun for Mid-Range F-TR and it does well for me. Krieger fitted one of their excellent barrels to one of my uppers and I assembled the lower with a Geiselle trigger and a Magpul PRS stock and some other accoutrements.

To complement properly this wonderful rifle, I developed and then assembled in large quantities, a handload that I believe does it justice. Of course, the bullet I use could not be seated to mag length, but that's not an issue because F-class is all single load. I also did not relish having my carefully assembled loads with expensive long bullets violently cycle through the AR-15 mechanism. I place my cartridge on a Bobsled and I push it into the chamber before releasing the bolt.

I also used one of those fancy Sinclair Gen 2 bipods and never a Harris.

I discovered over time, that Lapua or Winchester brass made no discernible difference in the gas gun. The brass gets beat up some, but since I have a chrome silicon buffer spring and a carrier weight system device in the bolt carrier, the post-ignition brass massaging was diminished greatly. My brass only flies about 2-3 feet from prone.

After starting with Lapua in the AR, my next batch was Winchester and I saw no difference on the target; the scores were the same and increased some over time as you would expect. I do more prep work with Winchester than with Lapua, but since it gets mangled by the AR, that difference soon gets lost.

I F/L resize the brass with a small base Redding S type, tumble clean, prime I load and go.

The brass management issues above will be the same with your rifle and if you shoot from the magazine, you will probably notice variations for the first and last shot in the magazine. I would spend some time looking for a good powder charge, but make sure you have enough powder in there to cycle the rifle properly. I would not waste much, if any, time on bullet seating depth; in a hard cycling rifle such as the AR, and especially with uncrimped cartridges, that's a waste of time. I would also look for something around .004 in neck tension.

 

[spclark]

You're off to a good start, appear to know what's what when it comes to picking specs & components. What other 308's have you been shooting before adding the GAP-10 to your stable?

I really like IMR'S 8208XBR for my Palma activities but found it not as good with 185's as with the 155 Hybrids I shot last season. Your shorter barrel & lighter bullet may make the difference here so it'd be my first choice.

I'd also suggest discovering just how long your chamber is & where both bullets load to before they encounter the lands. There's a lot going on in a gas gun's mechanicals before the bullet leaves the barrel so single-loading with a mag in place (or other means to lock the bolt back & prevent cycling) may improve your ultimate accuracy. Loading for this practice, longer than mag-length (unless your magazine is really generous in that regard!) ought to work better than an extreme (> 0.060") jump.

 

[stool]

get rid of the primer and go with a std lr primer...i suggest tula or wolf.

it is mechanically impossible for the firing pin to HIT the primer before the bolt is closed.

you may see a slight dimple in the primer...but never enough to set it off...

go with imr4064 and the sie 175 mk and see what happens

rl 15 works well also...i am one of those guys that never got varget to work for me.

 

[SWThomas]

I use a gas gun for Mid-Range F-TR and it does well for me. Krieger fitted one of their excellent barrels to one of my uppers and I assembled the lower with a Geiselle trigger and a Magpul PRS stock and some other accoutrements.

To complement properly this wonderful rifle, I developed and then assembled in large quantities, a handload that I believe does it justice. Of course, the bullet I use could not be seated to mag length, but that's not an issue because F-class is all single load. I also did not relish having my carefully assembled loads with expensive long bullets violently cycle through the AR-15 mechanism. I place my cartridge on a Bobsled and I push it into the chamber before releasing the bolt.

I also used one of those fancy Sinclair Gen 2 bipods and never a Harris.

I discovered over time, that Lapua or Winchester brass made no discernible difference in the gas gun. The brass gets beat up some, but since I have a chrome silicon buffer spring and a carrier weight system device in the bolt carrier, the post-ignition brass massaging was diminished greatly. My brass only flies about 2-3 feet from prone.

After starting with Lapua in the AR, my next batch was Winchester and I saw no difference on the target; the scores were the same and increased some over time as you would expect. I do more prep work with Winchester than with Lapua, but since it gets mangled by the AR, that difference soon gets lost.

I F/L resize the brass with a small base Redding S type, tumble clean, prime I load and go.

The brass management issues above will be the same with your rifle and if you shoot from the magazine, you will probably notice variations for the first and last shot in the magazine. I would spend some time looking for a good powder charge, but make sure you have enough powder in there to cycle the rifle properly. I would not waste much, if any, time on bullet seating depth; in a hard cycling rifle such as the AR, and especially with uncrimped cartridges, that's a waste of time. I would also look for something around .004 in neck tension.

Thanks for the advice. I've fired 50 reloads through it loaded with Varget from the min to the max and they all cycled fine. Cycling isn't an issue currently, it's finding the load that is most accurate. I'm picking up what you're laying down about the Lapua brass. I'm sure I'll find that out and spend less money next time I buy brass.

 

[SWThomas]

You're off to a good start, appear to know what's what when it comes to picking specs & components. What other 308's have you been shooting before adding the GAP-10 to your stable?

I really like IMR'S 8208XBR for my Palma activities but found it not as good with 185's as with the 155 Hybrids I shot last season. Your shorter barrel & lighter bullet may make the difference here so it'd be my first choice.

I'd also suggest discovering just how long your chamber is & where both bullets load to before they encounter the lands. There's a lot going on in a gas gun's mechanicals before the bullet leaves the barrel so single-loading with a mag in place (or other means to lock the bolt back & prevent cycling) may improve your ultimate accuracy. Loading for this practice, longer than mag-length (unless your magazine is really generous in that regard!) ought to work better than an extreme (> 0.060") jump.

This is my first 308 rifle. I have a 30-06 bolt gun, but it's nothing special currently. I'm in the process of sending it to GA for a complete rework. That will be a special rifle when it's done.

I've already used a tool to discover seating depth to put me on the lands. Problem is, That load is nowhere near fitting in the magazine. I may load some up just to see how accurate I can make this rig, but I have no desire to single feed this rifle.

 

[SWThomas]

get rid of the primer and go with a std lr primer...i suggest tula or wolf.

it is mechanically impossible for the firing pin to HIT the primer before the bolt is closed.

you may see a slight dimple in the primer...but never enough to set it off...

go with imr4064 and the sie 175 mk and see what happens

rl 15 works well also...i am one of those guys that never got varget to work for me.

Thanks for the advice. Any particular reason not to use the CCI #34s other than higher price? I really didn't buy them out of concern for slam-fires. They were the only thing available when I went primer shopping.

I'll definitely be working up a load with 4064. I'll do the same with 15 if I can find any.

 

[SWThomas]

I would also look for something around .004 in neck tension.

Any suggestions on achieving that?

 

[Turbulent Turtle]

You're giving me whiplash jumping between two threads for the same issue. I will answer her and put a note in the other thread.

Reading your other thread, I see that you are discovering what I warned you about with respect to COAL and gas guns.

I was going to originally say that Dillon 550B and precision do not go in the same sentence unless there is a negative in between, but instead I just pointed our that I use a Redding F/L bushing die to resize my cases and then specified the minimum neck tension to look for.

You will have a hard time achieving complete and consistent control of neck tension without a bushing die. Buffing an expander ball down is going to be difficult because you want to make sure it's perfectly round or else you've just introduced another issue.

I use a small base Redding F/L Type-S bushing dies for my AR-15 based F-TR rifle in .223 Rem and also for my .308 Bolt ArrowBee F-TR rifle. I use Lapua brass in my .308 and I use a .335 bushing for that brass, looking for about .002-.003 of neck tension. I am a firm believer in good repeatable neck tension that will also hold my very long bullets firmly while I travel and move ammo boxes in and out of hotel rooms, when they might (and have) drop on the floor.

The best way to decide which bushing you will need is to measure the OD of several loaded rounds and then subtract the amount that you want to achieve and perhaps subtract another .001. For example, it is very possible that your current loaded rounds measure .338 or so. If you want .004 of neck tension you would look for a bushing of .334 or maybe .333. Brass has some spring back.

 

[SWThomas]

You're giving me whiplash jumping between two threads for the same issue. I will answer her and put a note in the other thread.

Reading your other thread, I see that you are discovering what I warned you about with respect to COAL and gas guns.

I was going to originally say that Dillon 550B and precision do not go in the same sentence unless there is a negative in between, but instead I just pointed our that I use a Redding F/L bushing die to resize my cases and then specified the minimum neck tension to look for.

You will have a hard time achieving complete and consistent control of neck tension without a bushing die. Buffing an expander ball down is going to be difficult because you want to make sure it's perfectly round or else you've just introduced another issue.

I use a small base Redding F/L Type-S bushing dies for my AR-15 based F-TR rifle in .223 Rem and also for my .308 Bolt ArrowBee F-TR rifle. I use Lapua brass in my .308 and I use a .335 bushing for that brass, looking for about .002-.003 of neck tension. I am a firm believer in good repeatable neck tension that will also hold my very long bullets firmly while I travel and move ammo boxes in and out of hotel rooms, when they might (and have) drop on the floor.

The best way to decide which bushing you will need is to measure the OD of several loaded rounds and then subtract the amount that you want to achieve and perhaps subtract another .001. For example, it is very possible that your current loaded rounds measure .338 or so. If you want .004 of neck tension you would look for a bushing of .334 or maybe .333. Brass has some spring back.

Thanks for the info! I hope I didn't hurt your neck too bad. My intent with this thread was to getting an overall picture of squeezing more accuracy out of my rifle. The other thread is neck tension specific.

 

[SWThomas]

The best way to decide which bushing you will need is to measure the OD of several loaded rounds and then subtract the amount that you want to achieve and perhaps subtract another .001. For example, it is very possible that your current loaded rounds measure .338 or so. If you want .004 of neck tension you would look for a bushing of .334 or maybe .333. Brass has some spring back.

That Redding Type S die seems like exactly what I'm looking for. Question: does that die have an expander ball? If so, how do you keep it from opening the case mouths more than you desire when using a smaller bushing?

 

[Turbulent Turtle]

It does come with a removable expander ball. This first thing I did when I originally got the die set is to remove the evil expander ball and get rid of it. The box does contain a plastic grommet to hold the decapping pin in the stem. Some people deprime their cases in a separate operation, I think that's a waste of my valuable time, so after I anneal the fired cases and clean out whatever residue my cases may have even though they never touch the ground, I just size and deprime in the same operation.

I do the same for my .223 brass coming from my FTR Ar-15, but I have been know to tumble those before sizing.

 

[Turbulent Turtle]

Also, if you do get the Redding bushing die, you might want to consider getting the small base variant.

 

[SWThomas]

It does come with a removable expander ball. This first thing I did when I originally got the die set is to remove the evil expander ball and get rid of it. The box does contain a plastic grommet to hold the decapping pin in the stem. Some people deprime their cases in a separate operation, I think that's a waste of my valuable time, so after I anneal the fired cases and clean out whatever residue my cases may have even though they never touch the ground, I just size and deprime in the same operation.

I do the same for my .223 brass coming from my FTR Ar-15, but I have been know to tumble those before sizing.

I see. With my specific rifle, the brass mouths sometimes get dinged up/bent. How would you suggest handling that with no expander ball in the die? Would the resizing with the bushing iron that out and make it perfectly round again?

 

[SWThomas]

Also, if you do get the Redding bushing die, you might want to consider getting the small base variant.

I'll certainly look into that. I only saw one type of full length bushing die from Redding and assumed it was the small based one. I was looking at Brownells.

 

[Turbulent Turtle]

I see. With my specific rifle, the brass mouths sometimes get dinged up/bent. How would you suggest handling that with no expander ball in the die? Would the resizing with the bushing iron that out and make it perfectly round again?

Geez, that also sounds like something I mentioned earlier. :grin:

My AR used to do the same thing and in my case (no pun intended) that was because the brass would hit the deflector bump on the side. When I installed the chrome silicon buffer spring and the CWS, the ejection pattern changed and the brass was only rarely hitting the deflector. I replaced the ejector (and extractor) springs with chrome silicon equivalents and the ejector was now a little quicker and the brass never hits the deflector.

You could also play with the ejector spring to see if you can cut a loop or two to better time the ejection.

However all that said, a mandrel would be great, if the ding is pronounced. If it's not too bad, the bushing will get rid of it.

 

[Turbulent Turtle]

Also, if you do get the Redding bushing die, you might want to consider getting the small base variant.

I'll certainly look into that. I only saw one type of full length bushing die from Redding and assumed it was the small based one. I was looking at Brownells.

This is the one I use. I got it from Sinclair some years back. Get the proper bushing(s) after measuring a few loaded rounds.

http://www.sinclairintl.com/reloading-equipment/reloading-dies/rifle-dies/redding-small-base-type-s-full-length-dies-prod36568.aspx?avs|Cartridge_1=CTT_308 Winchester&avs|Die Style_1=Small Base Dies

 

[stool]

do not get a small bass die..esp if you shoot a single lot of brass thru one rifle....a waste if time and energy.
a std base die will do just fine, and will save your arm a little.
a small base die is fine for moving brass from one rifle to another..but has no real need outside of that in a gas gun.

i load my competition 308 loads in a dillon 550b.
i use two tool heads.
clean the brass
one...deprime ..lee deprime die and size..neck bushing used with die set to move the shoulder back about .002.
clean again
two deprime(it ensures the flash hole has no debris,lee universal deprime die with end of rod rounded to not hang up on case mouth), prime...i add weighed powder at station two and seat at three ... redding and forster ultra micrometer dies.
my aramlite ar10t is about 1/2 moa at short range with these loads.

 

[SWThomas]

I see. With my specific rifle, the brass mouths sometimes get dinged up/bent. How would you suggest handling that with no expander ball in the die? Would the resizing with the bushing iron that out and make it perfectly round again?

Geez, that also sounds like something I mentioned earlier. :grin:

My AR used to do the same thing and in my case (no pun intended) that was because the brass would hit the deflector bump on the side. When I installed the chrome silicon buffer spring and the CWS, the ejection pattern changed and the brass was only rarely hitting the deflector. I replaced the ejector (and extractor) springs with chrome silicon equivalents and the ejector was now a little quicker and the brass never hits the deflector.

You could also play with the ejector spring to see if you can cut a loop or two to better time the ejection.

However all that said, a mandrel would be great, if the ding is pronounced. If it's not too bad, the bushing will get rid of it.

I gotcha. Sorry if I'm asking questions in circles. I'm a stickler when it comes to the details and want to make sure I understand things. I suppose I could go with an expander die and a turning arbor to iron out any bent mouths. Something like this....

http://www.sinclairintl.com/reloading-equipment/case-preparation/neck-turning/turning-expander-mandrels/sinclair-generation-ii-expander-dies-prod38807.aspx

Honestly, I think the design of that Redding bushing die is cool but flawed. Unless you remove the expander ball, what's the benefit of using a smaller bushing if the ball is just going to open it back up? They should really offer smaller expander balls to match their bushings.

 

[Turbulent Turtle]

Ok. Like I said, the expander ball is removable and disposable.

However, that stated, a bushing die can be used with an expander ball to minimize the work done on the mouth. By design, a regular die will reduce the mouth more than needed by some brass, relying on the expander ball to bring it back to a usable size.

Using a bushing die without the expander ball minimizes the work on the mouth and provides fine control of the neck tension.