I have been hunting quite a bit with my Grendel this season. I keep loading the same round over and over for each hunt. Yesterday I noticed multiple dents in the shoulder. This is not a new issue as we have discussed it in the past. I ran a sharpe line down a round and loaded it line up in the magazine. I charged the round into the chamber I a new dent appeared at almost 6 oclock from my line. Fired rounds dont have as noticeable dent but I can still see where it has been. After separating the upper and lower today I got out the old bore scope and was checking out chamber are and saw something interesting. It is pictured below. What do you all make of the triangular irregularity on the edge of the chamber mouth. It is in about 5 oclock position. My case dent culprit?[ATTACH=CONFIG]19326[/ATTACH][ATTACH=CONFIG]19327[/ATTACH]
11-23-2022, 11:17 PM (This post was last modified: 11-24-2022, 12:32 AM by Klem.)
Ted,
I don't think the dents are caused by that irregularity. 6'OClock from the pen line is the knife edge between the two feedramps. I get them on mine, but not as severe as your photo. If that case has been fired before, the smaller dent near the larger ding is likely a previous firing that has fireformed under pressure to the shape of the chamber. So fireforming is sort of fixing them for you, but not completely. By the time the case is stripped from the mag and gone past the knife edge it's lining up pretty square to the chamber, so that irregularity probably does not even touch the shoulder.
As for the irregularity, wondering how metal gets chipped off at that spot and can only think of the bolt slamming into it as part of normal cycling. Especially if the carrier is released without a round to slow it down. Less likely cleaning rod damage, but maybe if the barrel was predisposed to crack at that spot.
Thanks for the reply Klem. Th round in the picture had 4 different dents from being loaded and and reloaded during multiple hunting trips. That lot of brass is once fired. I always load 5 rounds in a 10 rounds mag. That shell feeds off the right side of the magazine. Taking one out this leading to left side of the mag feeding resulted in no dent. Running one rounds. Right side feed, no dent. Seems that more spring pressure is attributing, maybe, to dents. Also my exposed lead tips are being deformed upon loading. I had previously worked on widening the feed ramps and lessening that sharp spot but am still getting the dent
Yep, most probably the mag. The angle of the case becomes more severe the later it is released from the lip. It crashes into the knife edge as it pops up.
Kinda stinks that a 10 rd mag only half loaded would cause that. It is a 6.8 mag. I will switch out to a 6.5 mag for the rest of the season loaded with the same 5 rounds and see what happens
So it is a design issue with the feed ramp/ramp divider? Are not more people having this issue? My barrel is a 20 PSA stainless. Accuracy wise I dont have any complaints as I get .75 with my 120 gr pro hunter hunting load and .75 with 90 gr tnt. Just wish it wasnt so hard on the brass.I single loaded a round to hunt the other day just to try to lessen case damage.
11-24-2022, 10:26 PM (This post was last modified: 11-24-2022, 10:28 PM by Klem.)
TedBrewer5 Wrote:So it is a design issue with the feed ramp/ramp divider?.
You could say that. There are no dedicated Grendel barrel extensions that I am aware of. The shape of the two feed channels on extensions are designed for 223/5.56, which of course is a narrower case. There are posts on the Forum talking about widening the feed ramps with a Dremel to make for smoother feeding into the chamber.
In your case it may be an easier fix to play with the mag lips. Once you shave the channels it is permanent (so it better make things better). Maybe even include polishing the underside and edges of the lip that is causing the trouble. The deal is, the mag needs to release the cartridge more freely in your case, so it pops up earlier and presents more parallel to the chamber. The more it grips the case the more it gets pushed up and presents at an angle with the BCG ramming it into the knife edge.
That should fix it, but if it doesn't then a different brand of magazine might work.
I did the deemed work on widening the feed ramps a while ago when this issue first presented itself. Barrel is now bedded so I wont be popping it off in the short term but may revisit. I have bent the mag lips a little more during that time but you seem to be describing shaving the edges of the lips back some
TedBrewer5 Wrote:I did the deemed work on widening the feed ramps a while ago when this issue first presented itself. Barrel is now bedded so I wont be popping it off in the short term but may revisit. I have bent the mag lips a little more during that time but you seem to be describing shaving the edges of the lips back some
Polishing the surface and edges that makes contact with the case, not shaving/cutting. The edges might be burred, which is another source of friction.
Something you'd use to polish you car, or headlights. Wet and Dry fine grit sandpaper and can of WD40 (I use this to clean caked carbon off the tails of bolts). Liquid or cream car polish like Autosol with a cut will also work. If you have a Dremel that will be perfect.
Play with the feed lips with a pair of pliers till it releases earlier but still holds the cases.
I will try that. What do you make of info in the video titled
Magazine issue & fix 6.5 Grendel
Mast Gun Works
On YouTube. I was curious about the shape of the feed lip causing the round to kick out and and possibly pushing it more over the middle divider of the feed ramp thus causing the dent. I also get the tip deformation he talked about in the beginning. My deformed tip is an exposed lead tip. The one in his video is a polymer tip. Anyway seemed to make sense but might be a rabbit trail
I de-edge, blend, and polish my feed ramps unless the barrel extension has already been tumble-polished, like on the ones Ive gotten from Precision Firearms.
My brass ejects looking new unless shooting suppressed.
There are 2 major types of barrel extension designs for the AR-15 when it comes to feed ramp geometry:
1. Original rifle extensions
2. Colt 727/M4 extended feed ramps, that require a matching upper with lowered feed ramps (rifle uppers never had extended feed ramps). This was a band-aid for cyclic rate issues in the Colt carbines shooting high volume full auto in certain units.
The serendipity of the extended feed ramps was that they provided a nice feeding geometry for larger cartridges like 6.5 Grendel.
The central divider can be harsh on your brass if the edges are sharp, which is why I de-edge, lightly blend, and polish them.
I also polish pistol barrel feed ramps to aid in reliable feeding.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
Klem Wrote:Something you'd use to polish you car, or headlights. Wet and Dry fine grit sandpaper and can of WD40 (I use this to clean caked carbon off the tails of bolts). Liquid or cream car polish like Autosol with a cut will also work. If you have a Dremel that will be perfect.
.
With respect Klem,
I would not recommend using any abrasive or steel to remove carbon off the bolt tail. High end manufacturers go to great lengths to keep a tight tolerance in their bolt tail bores in their carriers and is one of the many benchmarks to determine a high end or low end bolt carrier.
When you use abrasives or metal to scrape off carbon from the bolt tail, you are also reducing the O.D. of the bolt tail. The space between the bolt tail O.D. and the carrier's bolt tail I.D. bore uses a small tolerance.
Minimum: .0015
Maximum: .0025
This is one of the reasons a bolt carrier will cause a rifle to short stroke, while a different bolt carrier will run fine in the same rifle..
A shiny bolt tail is an obvious clue to this practice..
I will soak the bolt tail in solvent and use a plastic brush if I feel the need to remove any carbon off the bolt tail.
montana Wrote:I would not recommend using any abrasive or steel to remove carbon off the bolt tail.
Montana,
I understand where you are coming from from your previous contributions. My thoughts are is that one can get a bit too persnickety about this. I come from a different mentality of challenging dogma. Having done this for years without issue I am comfortable with what works for me. These guns are more likely overgassed from the start, leaking gas throughout the system and in some cases requiring AGB's and heavier buffers to function. Over the years if you wear down a tail, and it will take years, there is still gas to spare.
One scraping tool I do like is the Botach (photo). Give it a couple of spins on the tail and it takes the majority of caked crud off. Then if you want it completely clean use the wet-n-dry. I use P1200 grit which is super-fine and with WD40. The WD40 helps remove the crud and cuts back (pardon the pun) on the abrasive nature of dry paper. Like I say, it works and has worked for as long as I have been shooting these things. It's like the military dogma of cleaning barrels after every shoot - I don't do this; it shifts zero, wastes time, and potentially wears out barrels.
[ATTACH=CONFIG]19328[/ATTACH]
By comparison, the Otis tool at the bottom of the photo is not much use at all.
I understand where you are coming from from your previous contributions. My thoughts are is that one can get a bit too persnickety about this. I come from a different mentality of challenging dogma. Having done this for years without issue I am comfortable with what works for me. These guns are more likely overgassed from the start, leaking gas throughout the system and in some cases requiring AGB's and heavier buffers to function. Over the years if you wear down a tail, and it will take years, there is still gas to spare.
One scraping tool I do like is the Botach (photo). Give it a couple of spins on the tail and it takes the majority of caked crud off. Then if you want it completely clean use the wet-n-dry. I use P1200 grit which is super-fine and with WD40. The WD40 helps remove the crud and cuts back (pardon the pun) on the abrasive nature of dry paper. Like I say, it works and has worked for as long as I have been shooting these things. It's like the military dogma of cleaning barrels after every shoot - I don't do this; it shifts zero, wastes time, and potentially wears out barrels.
[ATTACH=CONFIG]19328[/ATTACH]
By comparison, the Otis tool at the bottom of the photo is not much use at all.
Each to their own.
No problem Klem, I always enjoy yours and others perspectives.
The picture of the shiny bolt tail is a perfect example of what I was talking about..Olympic Arms used a straight cut, undersized gas tube, over sized gas ports and a haywire approach to their rifles too..The real dogma is the need to keep the bolt and carrier carbon free, which I think came from the early days of Vietnam when the ball powder of the time had a high content of calcium carbonate, which was suspected to clog up gas tubes and carriers. Then the white glove maintenance appeared...Just like long gas tube pipe cleaners, carbon scraping tools are completely unnecessary and can actually be detrimental..
Like you said, each to their own..
So I messed with both the 6.5 mag and the 6.8 mag. Used 400 grit wet dry paper to feed lips on both. The 6.5 was definitely not as bad offender as the 6.8 and only required slight feed lip adjustment. The 6.8 I had to do more work to do to get it to stop the denting. Both seems to be ok now but I am going to keep my eye on the 6.8 going forward. I also lowered to front edge of the magazine by 1/16 after observing that the 6.8 looked like the round might be
Contacting it
![[Image: ?u=http%3A%2F%2Fi1085.photobucket.com%2F...ipo=images]](https://external-content.duckduckgo.com/iu/?u=http%3A%2F%2Fi1085.photobucket.com%2Falbums%2Fj422%2FLRRPF52%2FDSCF0261.jpg&f=1&nofb=1&ipt=c0168a36dbe055f59d539016d400dca3f1d9015a4be08577a4e7bcc4c75cd3b8&ipo=images)
