Low pressure sign??? 300RUM

[Bushcraft]

I've been lurking and learning here for a couple years, but mostly contribute on Kifaru. I consider Kifaru to be the very best forum for backpack hunting. And, along those same lines, LRH is the very best forum for practical long range field shooting. The knowledge base found here seems to be unmatched with regard to long range shooting.

I generally prefer "getting close" when hunting, but really enjoy longer range precision shooting. The procurement of a new Remington Sendero II in 300 RUM last year was a bit of an outlier for me as I'm predominantly a backpack hunter and lighter is better when it comes to getting a long ways back into the high and lonesome. But, the long-range bug bit me and I wanted a decent long-range platform that I could eventually have converted to a 338 Edge by Shawn Carlock.

I originally posted my problem over there, but it occured to me that by posting my experience here, I would a) garner some better information and subsequent solution, and b) perhaps the thread would help others avoid the same problem.

Thanks in advance for your input! - Allen

Here is the cut-and-paste (with slight edits) from my original post over on Kifaru....

I've never seen this first-hand before and thought it best to post up a couple pics and background on the particular situation before hurting myself or someone else on the firing line.

.300 Remington Ultra Mag - brand spanking new Remmy Sendero II
Nightforce 5.5-22X56 zero-stop with NF rings and bases, DE level and ADI
The usual anal retentive case prep including mild neck turn ( http://www.6mmbr.com/jgcaseprep.html )
A middlin' load of 90.7 grains of RE-25 behind a 175 SMK seated exactly to Sierra reloading manual specs.
Next step...off to fire-form the brass at the range and have some fun with this new rifle....

First round sent downrange was on the right. No chrony readout. Great.

Second round downrange resulted in the alarming oddity just below the shoulder. Again, no chrony readout. **** thing was acting up.

That's precisely when the fun stopped.

Has anyone ever seen this before? And, much more importantly, what to make of it?

My second post on the thread to clarify some questions:

I suppose I should have noted that this was brand new brass. Nope, couldn't have been a lube issue since I use a minimum of RCBS Case Slick and religiously wipe down the case when it is no longer warranted in the loading process. Besides, a clean case helps when it comes to writing the powder charge on the side with a Sharpie. Chamber and bore were pristine and ready to be (post-factory) de-virginized.

Oh, and Flamingo, the cases were not "smoked". The only micrometered difference in the two, other than the obvious dent in the side of the one (which eventually experienced a quick wipe and a look-see with a magnifying glass), is the slightest midgeon shown on the one on the right on the shoulder just under the neck. Pretty darn clean actually.

I just can't figure out why, all things equal, that this would have happened.

I'm a newbie when it comes to stuffing this much powder in a case this big and am admittedly a wee bit apprehensive about touching more of them off if this is a potentially serious problem. I'd prefer to keep my cheek bone where it's at. Same goes for eyes, hands, etc.

Should I be concerned or just chalk it up as a fluke?

Thoughts? Once again, thanks in advance.

Allen

 

[MTBULLET]

I would check and be POSITIVE of my charge weight. did any other rounds do this ?

 

[tackb]

it looks like a spot of oil on the case or in the chamber ?

low pressure wouldn't generally cause this , that normally leaves blackened residue around the neck of the case ?

your load seems fine , i would throughly clean the rifle and chamber not forgeting to dry the bore with a couple of patches with meths on then have another go ?

if your really worried about your handloads just buy a box of factory to try the gun and compare your loads to?

personally i wouldn't worry the next load will soon fire form it back to chamber size ?

 

[Bushcraft]

MTBULLET,

Good question.

I not only double check the powder charge before putting it into the case, but I also check the weight of all fully loaded cartridges before placing them in my MTM ammo boxes for storage or field use. Perhaps a bit on the anal side but it gives me peace of mind when I'm laying down behind my rifles.

I perform this final weighing step because I goofed very early on in my reloading career and only primed a .44 Mag cartridge which subsequently bound up the revolver. That was a real eye-opener. Weighing each completed cartridge before storage is a quick and easy final check and I've done so religiously with the thousands of rounds of ammo I've stamped out since. So, the odds would be very, very, very long that the charge was off.

I spoke with Sierra today and the fellow wondered if the RL-25 might have been an off batch. He was also perplexed as to why there was so little powder residue on the neck of the fired case that I hadn't wiped down (the one on the right without the dent).

I wonder if stepping up to a heavier bullet might be the way to go with this powder? I have quite a few 190 SMK's on the shelf that I'd hoped to build my go-to load with, so that is a readily available option. I've also got a pound of Retumbo that I thought might try if I didn't initially get the results I was hoping for with the RL-25, but, as per the thread, perhaps a faster powder might be the way to go....thoughts???

I'm really stumped on this one as this cartridge is a whole new animal for me, a significant departure from my much more sedate .308 and .223 loads. I wouldn't be as concerned if the guys out there that have been reloading forever weren't also stumped.

Allen

 

[MTBULLET]

h-1000 is my go to powder in the 300 RUM. found it more consistant and a little "quicker". However I tend to shoot the 168 BERGER VLD on everything now, paper to Elk, as I found this combination to be excellent in my PAC-NOR bbl'd rifle.

 

[outofayr]

I'll go back through my notes this evening - I've seen this EXACT symptom before. I was fireforming brass for my 6.5-06AI. I'll dig out the details and let you know...I don't think I ever figured it out for sure, though. IIRC, I ended up switching powders after that. I also got weird chrony readings and an "off" sound when I touched the round off that got the dented shoulder.

I'll post more once I've looked over my notes at home.

Brian

 

[SomeRumbum]

Allen- Please specify your primer. What primer are you using?

My load is 96.0 grains of RE 25, 180 Nosler Accubonds, Remington Brass, FED215m primers= 3250 fps and great groups out of my Sendero(s).

(it might be the scope. Please send it to me for 6 months for evaluation purposes. ).

Seriously, it seems to me it could only be in the chamber unless you are getting some kind of hang fire due to improper primers. Must be in the chamber if not.

 

[Bushcraft]

SomeRumbum,

Sierra's recipe suggested a Rem 9 1/2 M primer. I used a CCI Magnum Rifle. Can't imagine this being the culprit and nor could the folks as Sierra.

I might buy the argument that there was something foreign in the chamber if I was out in the boonies with wind and debris blowing around to beat hell AND if I noticed any (abnormal) resistance when closing the bolt on the second round. Since I was in a clean, rifle range environment shooting from a bench and felt no resistance, I think we need to dismiss that as a possibility.

Same goes for lube in the chamber since this was the second round. If excessive lube was the issue, which it couldn't be since the rifle had been cleaned, to include barrel, chamber and lug recess, I think it would/should have more likely occured on the first round.

Thanks,

Allen

 

[outofayr]

Allen:

I went back through my loading notes last night. My dented case (wish I had taken a picture - looked just like yours) was the 16th one fired that morning. I was doing load workup on my 6.5-06AI using 120gr Nosler BTs and RL22.

Everything was progressing normally, and I was just approaching what I thought would be a max load. The first load from that charge weight gave an error reading on the chrony. Not unheard of with the cheaper Shooting Chrony, but fairly rare for mine to give an error. Case looked fine, bolt lift was fine, primer just starting to flatten. I figured a cloud had blocked the sun or something, causing the chrony to misread, and sent the next one downrange. This one sounded "different" and got no chrony reading again. When I ejected the case, bolt lift was fine, but the case was dented just like yours...I stopped firing right then.

I eliminated case lube denting, as these had only been neck sized with dry lube, then tumbled clean. The round was perfect when it went in, but dented to heck when it came out...

The chamber was fine; I looked right then, just to be sure, but had no problems with previous 15 shots. Back home, I decapped that piece of brass and found a particle of tumbling media partially blocking the flash-hole. Must have been it. I've been anal about double checking that ever since, and have never had another problem with it. I chalked it up to hangfire/delayed ignition of powder charge....

Best of luck,

Brian

 

[MontanaRifleman]

Allen, I have had that happen about 2 or 3 times now, out of a couple of hundred hand loaded rounds, in my Sendero (older version) 300 RUM. One was not quite as large as your dent (almost) and the other(s) a little smaller. I have no idea why it happened other than there may have been something in the chamber or on the case. They were warm loads of Retumbo and not sure if it was 180 E-Tips and/or 210 Bergers.

My brass is also well prepped, turned and trimmed necks. Fed GM215M primers.

I will tell you this... I loaded the cases back up and I very clearly remember the larger dented one resulting in about a 6" flier at 427 yds. The dent came right out. If you want to reuse the brass, put it in your fowler pile until it is fireformed out again.

-Mark

 

[Bushcraft]

Thanks fellas. Great input. I just knew that this must have happened to other shooters on this forum. Unfortunately, it's seemingly still a mystery as to the cause.

I'm going to try launching the 190 SMK's with both RL-25, Retumbo and maybe H-1000. I think I've got 500-600 of 'em on the shelf anyway...might as well get busy and figure out what this (as yet) safe queen really likes to bang steel with out past 1k.

Thanks again,

Allen

 

[paleohntr]

Well I just went through this today. 700P in 300 RUM, 155 bergers on 90 grs of H4831 sc. With the problems finding primers over the last year I ended picking up a couple K of Rem 9.5 M, my original load was with WLRM primers. I had 8 rounds of the Winchester primed rounds left. I fired 2 w's to foul, after a brief cool down fired a rem. round, got that big case dent. WTH? Fire a W round looks fine, fire a R round big dent, alternate ad nauseum. Other than the dents and being 2" R-2" D, the R 9.5m shoots an identical little bug hole. The primers are the only variable that's changed. Looks like I need to hunt down some WLRM primers, even if it means eating a hazmat shipping charge.

 

[taly01]

unless you are getting some kind of hang fire due to improper primers

I agree, I was often getting the exact same case dimple near the neck as in your pictures with the first 1-2 shots in a clean barrel using CCI BR2 primers and 4831SC in a 6.5x55.

In hammer and bench testing the primers I found 1 in 3 was much weaker than "normal", I just think I had a bad batch, I chucked that brick of primers :cry: and got some RLRM, no problems with case dimpling anymore.

IMHO the case neck dimple is caused by too weak primer to ignite a slow powder completely, then the powder grains ignite a few inches down the barrel and suck the case in?

Anyway 300RUM almost certainly needs Fed215 primers.

 

[capt.d]

I have had one event like this while loading for a 7mm ultra. A buddy purchased a used Rem 700 and after a thorough cleaning and inspection I discovered his rifle had what I thoucht was an abnormally long throat. Be it from a huge amount of free bore from factory or the previous owner melting quite a bit of the lands out of it, a 160 gr. accubond would not touch the lands until well out of the case mouth. I thought it was odd as my Sako does not have near this much freebore. We just seated them to mag length and loaded several diferent charge weights of Retumbo. The first round with book start load went across the chrono rather underwhelmingly i thought but no strange sounds or other conditions were observed. Upon opening the bolt I went numb as I saw the case that flopped out! Just below the shoulder were dents almost identical to yours but five of them all around the case, however, there was alot of black on this one. After much thought and discussion I determined that it had to be due to the low "start" load and extreme jump to the lands. What I believe happened is that upon firing while the bullet was "floating" in thin air before engaging the rifling, the low charge of powder did not develop enough pressure to expand the case to chamber dimensions to form an effective seal and some pressure caused the case to deform inwards/ implode somewhat. Upon reaching this conclusion we moved up to the next charge weight with me driving, as it was my conclusion, and never had a hiccup again all the way up to book max. Low charge weights in those big cases are no good, combine that with his long throat and I believe book start was too low for his particular situation as I have never seen it before or since. Could be a hair brained conclusion but makes sense to me.