28" Krieger barrel with gas hole in barrel about .090. Gas block extended 2 inches further out barrel. Mega milled upper with Young Manufacturing side charging bolt carrier. Gas block is JP adjustable. Stock is rifle length with stock spring and 150 gram buffer. Using 28.5 grains 8208 with 123 AMAX.
Took to range 2 weeks ago to break in barrel with the old one and clean. Figured I would have to adjust gas block. The best I could get was for the bolt to catch on the empty magazine about 3/4 open. Could not get to lock by the bolt catch except by hand with empty mag. At this time I had a lite buffer and heavy spring.
Went and bought heavy buffer and stock spring and went to range last week to try again. Same problem and same result. Took to gun smith and we checked everything out. Even changed gas block to the one that came with the barrel from Krieger. He has a gun range so we could fire after any change. We tried several combinations of spings and buffers and the results varied from short stroke to the bolt catching on the mag. Never got but a few clean ejections and never ejected and feed a new round. Can turn gas down and hand eject brass and then release and it loads just cannot get gas system correct.
He was busy so I came home and got on line to research gas systems. Took rifle apart and checked everything from the alignment of the gas block,gas tube blockage, gas tube to gas key alignment, gas key to bolt holder, to the washers on the bolt. Could not find a problem. Would figure that the gas hole in the barrel at .090 would be enough but now I am starting to wonder.
Any other ideas? Thanks.
I would be dropping my charge a couple of tenths at a time until it stops short stroking. Powders vary by lot, by ambient temperature and primer choices factor in as well. I love 8208, but it is not necessarily as temp stable as some other powders I use. Just an idea.
Hoot
Hoot, I should have added that I have tried from 27.5 , 27.75, 28, and 28.5 gr. of 8208 using Lapua brass and Rem 7 1/2 primers. We tried these at the range and at the gun smith.
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09-27-2011, 03:28 PM
(This post was last modified: 09-27-2011, 03:31 PM by Drifter.)
Try a slower burning powder. 8208 is relatively fast for the Grendel. It's the most likely powder to short-stroke in the 18" midlength and 20" rifle-length systems that I've used. (The midlengths would likely function okay with 8208, but adjustable gas blocks had been turned down.)
Also, a heavier buffer would increase the likelihood of short-stroking.
A good gauge for tuning a system is to keep a few factory rounds onhand. I usually have a few AA 123gr Scenars and Hornday 123gr Amax factory rounds with me when doing initial trials. Besides tuning the system based on these rounds, it's been my experience that the barrel will show some indication of which bullet it likes best, and that's the first bullet that I focus my handloading efforts on.
Drifter
8208 lights off pretty easy. Got any BR4s you can try instead of the 7 1/2s ? Again, just an idea.
FWIW: My 24" loves 8208 and Amax 123s up until 29.5 at moderate temps, but starts SS at hot and 30.0 at cool temps, but starts SS at moderate and above temps. I also use 7 1/2s, but Hornady brass.
Hoot
Drifter Wrote:Try a slower burning powder. 8208 is relatively fast for the Grendel. It's the most likely powder to short-stroke in the 18" midlength and 20" rifle-length systems that I've used. (The midlengths would likely function okay with 8208, but adjustable gas blocks had been turned down.)
Also, a heavier buffer would increase the likelihood of short-stroking.
A good gauge for tuning a system is to keep a few factory rounds onhand. I usually have a few AA 123gr Scenars and Hornday 123gr Amax factory rounds with me when doing initial trials. Besides tuning the system based on these rounds, it's been my experience that the barrel will show some indication of which bullet it likes best, and that's the first bullet that I focus my handloading efforts on.
I was wondering about the 28" and powder. Was going by what has been said on this site about 8208 and did not look at chart to see where it was. I have always liked Varget for the 5.56 and I also have some VV540 that is slower. Was also thinking about getting a few factory rounds just to see.
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Varget is too slow. I'm a little surprised by this issue, since I shoot a 28" Satern, running 8208 behind 107 Sierras, 123 Sierras, and 123 AMAX's and I've never had a problem. My loads are right in that range, so......
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bwaites Wrote:Varget is too slow.
It's burn rate isn't too slow, but perhaps you're referring to the velocities it produces in the Grendel cartridge. It's a shame more can't be squeezed in the case.
For the OP, a supposedly temp stable powder that produces decent velocities and seems to be a little slower burning versus 8208, you might consider trying AR-Comp. It's burn rate should be comparable to Varget, but with higher resulting velocities. My setups will sometimes short-stroke with 8208, but never with AR-Comp.
Drifter
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Drifter Wrote:It's burn rate isn't too slow, but perhaps you're referring to the velocities it produces in the Grendel cartridge. It's a shame more can't be squeezed in the case.
For the OP, a supposedly temp stable powder that produces decent velocities and seems to be a little slower burning versus 8208, you might consider trying AR-Comp. It's burn rate should be comparable to Varget, but with higher resulting velocities. My setups will sometimes short-stroke with 8208, but never with AR-Comp.
I should have been more specific. You can't get enough of it in a Grendel case to give decent velocities. Varget is a GREAT all around powder, just not effective in the Grendel.
.308's, though, its awesome!
You seek escape from pain. We seek the achievement of happiness. You exist for the sake of avoiding punishment. We exist for the sake of earning rewards. Threats will not make us function; fear is not our incentive. It is not death that we wish to avoid, but life that we wish to live. - John Galt
bwaites Wrote:Varget is too slow. I'm a little surprised by this issue, since I shoot a 28" Satern, running 8208 behind 107 Sierras, 123 Sierras, and 123 AMAX's and I've never had a problem. My loads are right in that range, so......
Thanks for the input, I knew I had seen where 8208 had been used in 28" with no problems. Is the gas block on the Saturn placed 2" further out like mine or is it in the same place as a 24"? Cannot remember if Saturn had extended the gas block.
After looking at "Another Grendel that won't ..... My next question was to be what size should the port be on the barrel? I am starting to wonder if mine was too small as it is only .090.
Brick,
Bwaites's 28" has a standard rifle-length gas system, which provides more dwell time. I would think that an extended gas system is more appropriate for a 28" pipe, since heavier bullets will create stresses on cases that wouldn't exist in a rifle-length gas 20"-24" system. There is one other area you need to check that can cause short-stroking, but I doubt this is your problem unless you've been in heavy rain or submersed your fire stick: The receiver extension tube screw has an air bleed/drain hole in it, which also holds the stock to the tube. If that is clogged, it can cause short-stroking in the system, since you now have a pneumatic recoil reduction chamber in the extension tube.
I would also try it with a standard rifle recoil spring, and standard 5.2 oz rifle buffer. After that, you might start looking at opening your gas port, which is probably the direction you'll go since the Grendel uses larger port diameters than the 5.56. Since you have an adjustable gas block, if you have a larger port on the barrel, you can still control it with your gas setting screw, so I wouldn't worry too much when it comes time to open the port. Also think about how you will need more gas flow in the winter, when the temps are lower.
As far as the Vihtavuori 500 series powders go, they are bad news for auto-loaders, and are known for eroding throats quickly. The velocities, while very fast, are often erratic, and I've seen crazy extreme spreads with them in my .260 Rem. Since you have such a long pipe and an extended gas system, you can benefit from slower powders.
LRRPF52,
Thanks for the info--I am now using standard spring and 5.2 oz rifle buffer. I will check the stock as it is a spacegun stock and I do not know what screw was put in there. I was leaning toward drilling the port larger and as you say I have the adjustable gas block so I can keep it in check.
Did not know the VV 500 series powders were so bad. I had used in 5.56 and had gotten good results but had gotten better results with Varget as far a groups. Too bad Varget will not work with Grendel. Will see if I can find an extruded powder that will fit the bill.
LR1955 related to me that his gunsmith has seen high power shooters with clogged gas systems in AR15's using N500 series powders. The high velocities are attractive, but there is a price to be paid.
I would just suggest getting some factory ammo and get your gun tested and running with those and then work on reloads later. Plenty of time for that. But if it wont work with factory then you know it has nothing to do with your reloads.
Wolff also makes a reduced-power buffer spring that may be worth testing before attacking the gas port.
LRRPF52 Wrote:LR1955 related to me that his gunsmith has seen high power shooters with clogged gas systems in AR15's using N500 series powders. The high velocities are attractive, but there is a price to be paid.
Residue is my only beef with VV powder I tried. You should see the crud in my chrony after shooting the stuff. Looked like I had been fire forming with cream of wheat filler. It was not unburned powder as I collected a pile of it and laid a match to it with no resulting combustion. I can not say it clogged my gas system though, but then again it was N110 not one of the N5xx powders.
Hoot
My question is ....... does the rifle shortstroke using commercial ammo or just with your reloads?? I would shoot some wolf through and see if it still short strokes. If it functions fine with the wolf (or hornady or whatever), then you don't need to mess with the make up or your rifle.
Crap ...... Kamrr beat me to it ...... LOL.
Finally got a chance to shoot some today. Had taken the bolt out of the end on the buffer tube to release pressure and had picked up some Hornady ammo. On the first shot it locked back. That was the only time that it worked. Shot 10 rounds of factory ammo and only lock open once but it did eject each time. Changed springs and buffer to several configuration and still the same thing, ejection of brass but no lock back of bolt.
I brought the rifle home and drilled out the gas hole in the barrel to .106. Will go tomorrow to range and recheck to see if function is ok.
Drilled the gas port in barrel to .106 worked fine. Even went with a stiffer spring and lighter buffer with no problems other than being left handed and have hot brass land on you neck-Ouch!!! Thanks for all the help and pointers.
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