Proper recoil spring diagnosis?

[Whelenon]

The Grendel is my first AR so I'm still learning and trying to improve the performance of my rifle. From reading the Grendel Forum where your brass lands seems to indicates if the rifle is recoiling too much or too little. Is this correct or not?

If so, my Grendel is kicking brass out in front of me at 1:30 about 4-8'. I'm using both factory and reloaded ammo out of a 16" mid-length barrel. Shooting one round at a time occasionally the brass doesn't clear the receiver and ends up lying on top of the magazine follower. The recoil seems a little weak but up until now my bread and butter gun was a 35 Whelen. Does this indicate the proper recoil spring or is there something else going on?

[LRRPF52]

Sounds to me like a weak ejector possibly. Push down on your ejector plunger. It should resist your force significantly. That is odd to have a 1:30 ejection pattern. 3:00 or thereabouts seems more common if your upper has a brass deflector, as most do. Different charge weights and operating system balances will produce different patterns, but an ejector can make the biggest influence on whether the spent case clears the ejection port or not. Since you had a case left on top of the magazine, that indicates to me either an ejector or extractor issue, but since it was extracted, that points more to the ejector.

Give us a break down of your rifle's components, to include barrel/gas system length, bolt carrier weight, recoil spring and buffer types (weigh the buffer if you have to), adjustable gas block or not, and cartridge components, to include charge weight and bullet type/weight.

[QuadCam]

I have had similar ejection patterns as Whelenon; I also have a 16" midlength Grendel. I have had a few final rounds end up sitting in the upper reciever. I also have had some shells eject in the 1:30 area and it tosses them about 4-6 feet. I have also had shells that ejected at 3:00 only a foot or so away from the rifle.

When manually ejecting a round, they all eject and never flop around in the upper receiver, but they only get tossed about a foot or less to the side. It has been suggested by other on this board that I have an overgassed gun after seeing pictures of the ejector and extractor marks on the case heads. To slow down the ejecting process, I read various threads on these boards (and others) and it seems that a heavier buffer (around 5.3 ounces) is the way to go on a grendel. I haven't tried this out yet as I think I may also have a chamber and/or headspacing issue, too. I've been in contact with AA about remedying my rifles ailments......

[Drifter]

Sounds like overgassed to me. A heavier buffer, buffer spring, and / or BCG might help. But based on my experience with midlength 18" 6.5's, the best remedy is an adjustable gas block.

With the lo-pro PRI version, I usually shut the gas completely off, then back the screw out 1/4 to 1/3 turn, using a dab of Rocksett on the screw threads (and allowing it to dry). Doing this will make you think that there's no way the weapon will function, but that's what works for me.

I would like to see 6.5 barrel makers use smaller gas ports on midlength systems, but maybe my experiences are unique...

[Whelenon]

Sounds to me like a weak ejector possibly. Push down on your ejector plunger. It should resist your force significantly. That is odd to have a 1:30 ejection pattern. 3:00 or thereabouts seems more common if your upper has a brass deflector, as most do. Different charge weights and operating system balances will produce different patterns, but an ejector can make the biggest influence on whether the spent case clears the ejection port or not. Since you had a case left on top of the magazine, that indicates to me either an ejector or extractor issue, but since it was extracted, that points more to the ejector.

Give us a break down of your rifle's components, to include barrel/gas system length, bolt carrier weight, recoil spring and buffer types (weigh the buffer if you have to), adjustable gas block or not, and cartridge components, to include charge weight and bullet type/weight.

I'll try and answer your questions as best I can:
Ejector and extractor both look as expected with good spring tension.
Receiver is a YHM w/brass deflector.
YHM upper w/16" AA barrel and a mid-length gas system, non-adjustable.
The bolt carrier weights 9.0 oz w/o bolt and 11.0 oz w/bolt
The buffer weights 3.0 oz.
Spring and buffer type? Don't know, I'm not familiar with different types.
Buffer spring is 10" long and 7/8" dia.

Last time out shooting I had my first Grendel reloads.
Lapua Brass, Rem. 7-1/2 Primers, H322, Sierra Pro-Hunter 120g's
Lightest load 23.5g
Heaviest load 25.5g
I've also shot both AA and Hornady factory ammo.
I've had this problem with all ammo, but more often with the reloads.

[warped]

Your buffer is too light to start, not the whole problem but it may be a cumulative one.

Your buffer should ideally weigh as much as a rifle buffer, it increases dwell time and softens recoil, all kinds of good stuff.

Weight is between 152 and 155grams to be exact.

Buffers should not be viewed as ounces because a subtle difference does quite a bit and still no change it apparent weight in oz.

Anyways Bruce, let me know if I can help you in some way.

[michaelmew]

Your buffer is too light to start, not the whole problem but it may be a cumulative one.

Your buffer should ideally weigh as much as a rifle buffer, it increases dwell time and softens recoil, all kinds of good stuff.

Try a Spike's Tactical Heavy Buffer. http://www.spikestactical.com/new/z/...fer-p-201.html I recently switched and have had good results. I am planning on using them in all my AR's

-michaelmew

[glane5910]

My 338 Federal was doing similar but it was undergassed. The port had been drilled for a 308, not 338.

[QuadCam]

Try a Spike's Tactical Heavy Buffer. http://www.spikestactical.com/new/z/...fer-p-201.html I recently switched and have had good results. I am planning on using them in all my AR's

-michaelmew

Spikes now has a heavier t3 buffer which is closer the weight that warped recommended.

http://www.spikestactical.com/new/z/lower-parts-spikes-stt3-heavy-buffer-p-708.html

I chose to go a different path the the Vltor A5 Emod combo. It is quite interesting. Uses a slightly longer buffer tube (about 3/4" longer than a car stock, longer spring, and a rifle weight buffer (5.3oz). Basically, you get the adjustability (7 positions) of a carbine stock with the benefits of the longer rifle buffer system. You can also buy the parts separately if you don't need the stock.

http://www.vltor.com/emod-a5.html

[LRRPF52]

Yup. Your buffer is way too light for the Grendel and especially 120gr pills. I would try an H2, ST-T2, and even an H3. You have a carbine spring, and most likely an AR15 bolt carrier at 9.0 oz. I just weighed an M16 bolt carrier and it was 9.4 oz., and I also weighed a Bushmaster (shaved) AR15 bolt carrier at 8.7 oz. Tactical machining has a great deal on H2 buffers right now for about half the market price.

https://www.tacticalmachining.com/

What happens with a lighter weight operating system is that the bolt carrier moves too quickly to the rear, and not enough gas pressure builds in that chamber formed by the back of the bolt gas ring flange, gas rings, and carrier recess for the bolt. As it moves rearward too quickly, it bleeds gas out the vent holes in the carrier that you can clearly see from the ejection port, and you get a short stroke sometimes. This is where the balanced operating system needs either more weight to resist the gas impulse, or less gas. I would suggest more weight to the bolt carrier and buffer.

A fast unlock time will also run your brass harder, so you definitely need to adjust your system to provide the correct balance for the gas you're running through it. The adjustable gas block would be a potential solution to that particular load, giving you milder handling, but I would still recommend starting with your carrier and buffer weights first. Those 2.9-3.0oz carbine buffers are good for .223 carbines pushing 45gr bullets, and maybe 55gr through a 14.5" pipe with carbine gas system, or shaved AR15 carriers pushing the lighter loads. They are not anywhere near ideal for the Grendel or even 5.56 NATO loads in carbines.

[Whelenon]

Thank you all for the information. I will definitely start with the heavier buff. To summarize, I'm overgassed and underweight, correct?

I've been smithing for a lot of years but until just recently never got into the AR's. Both the AR and Grendel are a blast not to mention the most accurate rifle I've owned. It''s easy to work on plus the versatility and available options are just amazing. The information and synergy on this forum has been the icing on the cake. It's made my experience with the AR/Grendel a real treat. Thanks again.

[LRRPF52]

I would say you're properly-gassed, and under-weight. Manufacturers need to cut gas ports for reliability, while the customer can tune the recoil and gas system to the loads they might end up favoring. The Grendel is a fun gun to load for and shoot, and the AR is the most versatile firearm design with market support and user-configurability. It's the big boy's erector set...that also spits bullets.

I would get either an M16 weight bolt carrier or carrier weights from Tubbs, and a heavier buffer. You could also have someone like Warped provide you with a proper weight buffer for the Grendel. I've used a Spike's ST-T2 tungsten powder-filled buffer on my 16" Grendel from the start, and have had zero issues of ejection or extraction with mild to hotter loads, in the 123gr, 120gr, and 100gr bullet weights with several different powders. I use an M16 bolt carrier, standard carbine recoil spring, and plenty of Slip 2000 EWL.