Overgassed rifle with IMR 4895?

[USMAGator]

This has me stumped and I'm hoping that some more experienced shooters and reloaders can point me in the right direction here.

I got an OBR(7.62 18in) last fall and have been enjoying playing with different reloads to see what gives me the best results. In shooting factory ammo (FGMM 168s) and previous reloads(using Varget, BL-C(2), and H335), the rifle has thrown brass very consistently to my 4:30-5:00, about 4 feet from the gun. In the past week I have been trying some loads using IMR 4895 and, with each load, the rifle is now throwing the brass at 1-2:00. For comparison's sake I fired a string of FGMM yesterday afternoon and ejection was to my 4:30 (normal position).

I've read that forward ejection can be a sign of overgassing, but I'm not seeing anything else to indicate that...no abnormal swipe marks or rim damage. The brass is actually only being thrown a few feet (2-3), not as far as normal ejection from this gun.

For reference, the loads I've been testing are using 1-2x fired LC brass, IMR 4895 (40.0-42.0 gr), CCI #200 LRPs, 168gr SMKs, OAL of 2.795. The only pressure sign I'm seeing is very slight cratering of my primers at 42.0 gr.

Any help or experience with this would be appreciated!

 

[R.O.U.S.]

Re: Overgassed rifle with IMR 4895?

I don't know how much applies, but I purchased a 16" 7.62 OBR recently. I have 280 rounds through it. 147 grain ammunition ejects towards 3:00. I fired Hornady 168 grain BTHP and noticed that everything was flying towards 1:00. I was getting slight cratering on some of the shell casings I recovered. My OBR has a rifle length extension with a H2 buffer, red spring, and a spacer.

 

[elfster1234]

Re: Overgassed rifle with IMR 4895?

Not sure if this helps you out or not brother, but mine ejects to about 4oclock. I've done work up loads all the way from 39.5, 40.0, 40.5, 41.0, 41.5, and 42.0 and for some strange ass reason my LMT lovessssss varget @ 40.5.... For 100yards 40.5 varget is all I need, but I might need to look into a different load if I was pushing 500yards plus.. I've seen guys with loads wayyy past max loads (like 45 and even 46 in which I think is absolutely crazy in a gas gun, maybe a bolt action)... I could really use a chronograph also.. One of my next purchases.

How old is the buffer spring / how many rounds on the buffer spring do you think? Just wondering.

 

[disdp1]

Re: Overgassed rifle with IMR 4895?

Was at the range today. Ran Varget @43.5grns for 2702 and H4895 at 42.8 grains running 2703fps. I'm shooting a dpms 308 w/ a 24" fluted bull. All my brass ejects at the 1:00 position. I will be trying a 2600fps load mid week and see what the ejection direction may be. Today I put several 5" groups at 514 yards w/ a 2.2milrad correction. Additionally, I'm sighted in at 300 yards and need to shoot 4.5"s low at 1 & 200 yards if I want to shoot center of target. Just reviewed the brass and do not see any overpressure signs in any of the 50 rounds that went down range today. These loads are HOT. If I don't hold the monster firmly I just barely brush my eye lid with the scope. So, coming down a grain should only help accuracy. I'll let you know.

Regards,

 

[lazy21]

Re: Overgassed rifle with IMR 4895?

I had a overgassed SASS(suppressed) and sent it off to a guy named Thomas and he made me the bad ass three position gas block

 

[USMAGator]

Re: Overgassed rifle with IMR 4895?

Thanks all for the responses. This just has me scratching my head a bit because it is a very definite shift in ejection from an otherwise consistent pattern. The groups with 4895 have been pretty inconsistent for this gun, especially compared to Varget with the same bullets, so I'll probably switch back to Varget and save the 4895 for my Garand.

@Elfster, the buffer is the original and has roughly 650-700 rounds on it, I haven't kept an exact round count.

@Dave, sounds like some good shooting, I wish I had somewhere near here where I could shoot that far! Let us know how it goes on the next outing...my best groups with Varget have been in the 43.0 range (assuming you're talking about 168gr pills), hot but not showing anything past mild primer cratering.

@Lazy21, do you mind telling me how the overgassing showed itself in your case? That looks like a slick fix, but I'm hoping mine won't need anything that involved. Sidenote, I may be in touch with you once USO gets their 1-8x out to see what you can do for me!

 

[Tx_Flyboy]

Re: Overgassed rifle with IMR 4895?

Gator,

As long as:

1. The rifle ejects reliably every single time
2. Your reloads do not exhibit pressure signs
3. You are satisfied with the resulting accuracy of the rounds

Then it doesn't matter what the ejection pattern is.

Think about it. Depending on the type of powder, the amount of powder and bullet you are shooting, you may be "overgassed".

Slow burning powders and heavy bullets will produce higher port pressures than fast burning powders pushing lighter weight bullets. It is a phycical certainty.

Your gas port is a fixed orifice. It stands to reason that certain loads will be "overgassed"..if you are that worried about it, then invest in an adjustable gas block so that you can regulate the gas pressure cycling your bolt.

But beware of adjustable gas blocks...they will change your accuracy nodes. They did with mine.

The reason I put overgassed in quotation is because it is a word that is thrown about on the internet without a lot of people understanding what it means. Because the ar gas port is a fixed orifice, there is only one gas setting (pressure) at which the AR is optimized. Everything outside of that is either undergassed or overgassed. Some deviation upscale and downscale of this optimum is allowable as long as there are no real issues (cycling issues or rifle damaging itself irreparably)

Sorry for the long-winded post.

If you are not having any real issues, then just shoot your rifle and be happy.

Best.

 

[RufDog]

Re: Overgassed rifle with IMR 4895?

Good post TX. I believe Larue uses a proprietary port arangement that keeps one from using aftermarket blocks with good adjustability. (Someone correct me if i'm wrong) Also barrel changes are more of a pain due to a propreitary extension. No easy solution if you get to the point of being overgassed to the point of damaging things.

 

[raptor99]

Re: Overgassed rifle with IMR 4895?

I know you can hurt an M1A with hot loads but I didn't think you could hurt the AR10s with the hotter loads. Am I wrong on this??? What damage can you do if any??? Wouldn't a heavy recoil spring help?? Thanks guys!!

 

[USMAGator]

Re: Overgassed rifle with IMR 4895?

Flyboy - that makes sense and you're probably spot on. I just found it odd that the rifle would exhibit this behavior with just this one powder out of the options that I've tried. I don't think I'll be shooting with 4895 in this gun much more since the accuracy isn't matching loads with Varget. Thanks for the info!

Raptor - I'd guess that in an extreme case you could damage the BCG, but you'd probably see high pressure signs before it became a real issue. That's just my assumption though, and those can sometimes be dangerous

 

[Tx_Flyboy]

Re: Overgassed rifle with IMR 4895?

Rufdog,

Not sure what Larue uses, but its simply a hole on top of the barrel for gas to enter the gas tube and cycle the BCG...a fixed orifice like any on any AR barrel.

Raptor99,

You are correct. M1As and M1 are sensitive to port pressures because of a long skinny op-rod that can be overstressed. This is not the case with an AR-10/AR-15 type rifle. My use of the term port pressure is simply to illustrate that when you have a fixed hole, there is a single setpoint where things are optimized. Hell, with certain powders and their temperature sensitivity, you may get away from optimum in either the winter or summer...point is ITS NO BIG DEAL.

Gator,

Choose your loads & powder based on the concept of "Suitable for the application" not ejection pattern. The ejection patterns discussed ad nauseum on the internet is an ideal, an optimuim is you like...but not all of us are dating sexy blondes and driving ferraris...that is an optimum, but not enirely achievable under all circumstances.

If you are that bothered by ejection pattern as to move away from a great powder, then I'll gladly take the H4895 off your hand...Just pay the shipping and Hazmat fees

Once again, if you are not having cycling issues, pressure issues, or anything untoward, don't worry about your ejection pattern.

 

[TonyAngel]

Re: Overgassed rifle with IMR 4895?

Yeah, loading for a gas gun can leave you scratching your head sometimes.

For what it's worth, I do believe that Federal uses a proprietary blend of 4064 powder. It is a good powder that gives good velocity. The drawback is that it's pretty temp sensitive. You might also want to try Reloader 15.

Reloader 15 has a burn rate slightly slower than Varget, but does give better velocity, so you might be able to back off of the charge a little and still maintain velocity.

 

[elfster1234]

Re: Overgassed rifle with IMR 4895?

I think there is a lot of truth to what flyboy just said. Yes, is it possible to have a bad buffer spring, yes.... but most likely not on a rifle that has only 600 to 700 rounds. Makes sense to me.

Elf

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">Gator,

As long as:

1. The rifle ejects reliably every single time
2. Your reloads do not exhibit pressure signs
3. You are satisfied with the resulting accuracy of the rounds

Then it doesn't matter what the ejection pattern is.

Think about it. Depending on the type of powder, the amount of powder and bullet you are shooting, you may be "overgassed".

Slow burning powders and heavy bullets will produce higher port pressures than fast burning powders pushing lighter weight bullets. It is a phycical certainty.

Your gas port is a fixed orifice. It stands to reason that certain loads will be "overgassed"..if you are that worried about it, then invest in an adjustable gas block so that you can regulate the gas pressure cycling your bolt.

But beware of adjustable gas blocks...they will change your accuracy nodes. They did with mine.

The reason I put overgassed in quotation is because it is a word that is thrown about on the internet without a lot of people understanding what it means. Because the ar gas port is a fixed orifice, there is only one gas setting (pressure) at which the AR is optimized. Everything outside of that is either undergassed or overgassed. Some deviation upscale and downscale of this optimum is allowable as long as there are no real issues (cycling issues or rifle damaging itself irreparably)

Sorry for the long-winded post.

If you are not having any real issues, then just shoot your rifle and be happy.

Best. </div></div>

 

[raptor99]

Re: Overgassed rifle with IMR 4895?

Thanks Guys, I have been having trouble getting a load to shoot consistant in my rifle. I tried IMR4895 and it shot well at 100yds but would open up considerably at 400+yds.

I tried the 175s with varget and had mixed results but thought I may have to stay with that until I tried my bolt gun load with 46grs of Varget in Federal cases with the 168s. It shot a lot better at long range and was much more consistant.

I know thats a faily stout load and was wanting something a little less for the AR but I don't shoot it all that much anyway so it will probably be fine for what I do with it.

 

[RufDog]

Re: Overgassed rifle with IMR 4895?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">Rufdog,

Not sure what Larue uses, but its simply a hole on top of the barrel for gas to enter the gas tube and cycle the BCG...a fixed orifice like any on any AR barrel.

Raptor99,

You are correct. M1As and M1 are sensitive to port pressures because of a long skinny op-rod that can be overstressed. This is not the case with an AR-10/AR-15 type rifle. My use of the term port pressure is simply to illustrate that when you have a fixed hole, there is a single setpoint where things are optimized. Hell, with certain powders and their temperature sensitivity, you may get away from optimum in either the winter or summer...point is ITS NO BIG DEAL.

Gator,

Choose your loads & powder based on the concept of "Suitable for the application" not ejection pattern. The ejection patterns discussed ad nauseum on the internet is an ideal, an optimuim is you like...but not all of us are dating sexy blondes and driving ferraris...that is an optimum, but not enirely achievable under all circumstances.

If you are that bothered by ejection pattern as to move away from a great powder, then I'll gladly take the H4895 off your hand...Just pay the shipping and Hazmat fees

Once again, if you are not having cycling issues, pressure issues, or anything untoward, don't worry about your ejection pattern. </div></div>

I consulted with 2 of my OBR owner friends & they said the OBR & HYBRID (whatever that is) have select-able gas blocks & they have a non standard port location. As I understand it, it has 2 ports. If it has a non selectable gasblock it is a normal gas port.

 

[RufDog]

Re: Overgassed rifle with IMR 4895?

I found out I am wrong about the Larue gas ports. Sorry guys.

 

[USMAGator]

Re: Overgassed rifle with IMR 4895?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">
If you are that bothered by ejection pattern as to move away from a great powder, then I'll gladly take the H4895 off your hand...Just pay the shipping and Hazmat fees

</div></div>

Haha no such luck! I'd gotten the 4895 to begin loading for my Garand and was curious about what kind of results I'd get in 308 with it.
It certainly won't be going to waste

 

[Tx_Flyboy]

Re: Overgassed rifle with IMR 4895?

Raptor,

Your groups opening up is a function of many things which may or may not have to do with your powder or rifle...I would not rule out your AR setup until you isolate the issue.

Anything from the list below can affect your group at distance.
1. Technique
2. Shooting set-up (shooting off Bipod instead of bags)
3. Picking the wrong load (the best load is not always the tightest...Google "OCW")
4. Scope/Parallax.

I say stick with it. Your AR will surprise you with accuracy once you get used to shooting it and iron out the remaining items above.

Gator,

Do a normal load development for your AR like you would a bolt rifle...pick your accuracy load based on the OCW method...the tightest group is not always the best.

It is likely you are not at your OCW or you maybe using too light a load. I mention the latter since you indicated that you bought your H4895 powder for your garand...if this is so, then perhaps you've subscribed to conventional wisdom out there that semi-auto rifles cannot handle full power loads.

I too have a garand, i've heard the dire warnings about slow powders and heavy bullets...I call BS on it.

Read this http://forums.thecmp.org/showthread.php?t=82742

and this: http://www.garandgear.com/index.php...mercial-ammunition-in-your-m1-garand&catid=39

Pay attention to the measured gas port pressures with 150gr loads and 180gr loads...

Best