Pressure Issues Early in Work-up

[Chris K]

Hey everybody, I have been reloading since 2006, I still consider myself new and reltively inexpierenced. I have never had any issues with safety or erratic results until I started loading for my GAP barreled 300WM.

This is a Win M70 action with a 24" Shilen 1:10 installed by Moon (Tim?) at GA. I have 400 hundred rounds of factory match ammunition from Hornady (178), Southwest and Corbon (both 190SMK) with no pressure issues and started loading 220 SMKs in once fired Winchester Brass. They are FL sized, trimmed, and set up with Fed 215M, IMR 7828 SSC set at mag length of 3.390 OAL.

At 72gr (3 grains under max from IMR) I got this on my case head with slightly hard bolt lift:


To me, this seems a bit early to be seeing what I assume is significant pressure, I stopped immediatley and and didnt go any further in my higher charged loads. Can this be a result of a match chamber being tighter than factory cut and I'm seeing early pressure? I need to chrono the 70-71.5 to see if my velocity is adequite for shooting 1000+, and if so I'll leave well enough alone.

Anyone else have rifles that hit pressure signs this early in development? Any advice is more than welcome!

Thanks

C_K

 

[FamilyMan]

I just ran into a similar situation with a 300wsm. I was 2 grains below max in three different books and had flattened primers, bolt swipe, and got my bolt stuck where I had to tap it with an empty mag to get it open. I don't know what the issue is yet so I am interested to hear some info on what to check to root cause it. I feel I was thorough in my brass prep and loading but we'll see
I was using H4350 with 190SMK's

 

[Chris K]

I just ran RL-22 and 190SMKs in a ladder up towards max and had no issues. Im going to load up 220's and H1000 tonight and shoot Wed. Maybe my stick no likey 7828?

CK

 

[insight3b]

I've had it happen when I worked up a load in the winter months/temperature and then used the same load in the warmer summer months and when I used the same powder but different lots

 

[Chris K]

its definitely not jammed, I don't have an OAL gauge. These are mag length, Im away from my bench or I'd get you a measurement...sorry...

 

[FLIGHT762]

Where's the bullet ogive in relation to barrel rifling?

This^^^^^^^^^^^^^^^^^^^^^^

its definitely not jammed, I don't have an OAL gauge. These are mag length, Im away from my bench or I'd get you a measurement...sorry...

SAAMI Maximum COL is 3.340" for the .300 Winchester Magnum. You said you loaded to 3.390" , your magazine length. You also have a custom barrel and you could possibly have a shorter throat than a factory rifle. If you haven't measured the distance to your lands, you don't know if you have jammed these 220's into them.

I have a short throated .308 Win. that would meet the lands A 2.790", slightly below the SAAMI maximum length of 2.800".

You could load a few to 3.340" to see if that helps. Temperature could be a factor, if you shot the loads in high temps. I'm not sure if the short cut IMR 7828 is a less temperature sensitive powder. Just something else to think about.

 

[MarinePMI]

Another vote for the ogive being too close to the lands.

This is a fairly common thing with radical wildcat fire forming, except it is done on purpose to get a good fire forming to the chamber. Cases almost always shows pressure signs sooner with the bullet either jammed into the lands, or close enough to the lands to be, for extents and purposes, jammed into the lands, causing early pressure signs...

 

[insight3b]

Something else to consider:
The chamber was probably cut at GAP for the 190gr FGGM SMK or the MK248 MoD O with the 190gr SMK so the leade is much shorter to decrease the jump for the 190's and now you are using 220gr with the ogive much thicker/fatter towards the meplat and jamming into the rifling

 

[Cncjerry]

I am running IMR 7828SSC with SMK 190s in my 300 WM and getting around 2700fps with 64gr and WLRM primers (note the M). I noticed pressure issues starting at 67gr of 7828 SSC with the 190's. I had been setting COAL to 3.34 then moved it up to 3.44 after measuring and my groups improved. At 3.44 the SMK (and 168s as well) are about .027 off the lands as near as I can tell. I am going to make a more sensitive gauge this weekend specific to the SMKs by drilling a hole in the back of a SMK on the lathe, soldering a thin copper welding rod that will then protrude from the back of a case and stopped with a collar. This will allow me to get a better feel for the ogive contact.

According to the Lee doc, the IMR 7828 loads should be from 75 to 80C, but other doc, including Hornady's book, has 7828 maxed at 72.8gr for a 190. The 220s are maxed at 69.9 (in red) for 7828 in the Hornady book.

By the way, I at first thought I was using too little powder and was thinking of adding instead of subtracting which would have resulted in a much larger problem.

As always with reloading, your mileage will vary. I am shooting a 26" barrel. You can PM me if you want to compare loads offline as I am fighting through my 300 WM right now. I get decent groups for me at 100yds, right around .6" using SMK 168s and 69gr of 7828 SSC with COAL at 3.34. Even though my gun can handle 3.44 COAL with 168's I didn't see much difference over 3.34. The 190's I will shoot at 64gr of 7828 and COAL of 3.44" after the multiple three-shot consecutive groups all less than .5" with 10mph wind at 100yds today. That is about my limit right now.

So the 168's averaged 2810fps with 70gr and the 190s averaged 2661 with 64gr but shot 2.5" higher for some crazy reason. I mean, why would a slower, heavier projectile hit higher on a well-bedded rifle?

 

[JGorski]

I just ran RL-22 and 190SMKs in a ladder up towards max and had no issues. Im going to load up 220's and H1000 tonight and shoot Wed. Maybe my stick no likey 7828?

CK

I always load RE22 in the 300WM, never had any complaints from the guys or their guns. And I never use 215s WLRMs work just fine.
get yourself some 178AMAXs and load up 75.5-76grs RE22, bet that shoots good for you with no pressure signs.

 

[Cncjerry]

Mtn, yes, I am loading low for a couple of reasons as my experience is lower is better for accuracy. A lot of people load for max smoke and that is another side of the hobby. Also, my .300 doesn't have a brake so low is easier on the shoulder. The reason I commented is like I mentioned above, I found the reloading sheets to be much higher than some books I found. I also think the SSC powders do burn faster oppose to what they say so the power curve is different.

 

[Aimsmall55]

GAP chambers are always really snug. That being said is this new brass or fire formed. Also as one fellow said, every GAP I own is cut to sammi specs. I've even got a 6.5 creedmor that is a lot shorter than sammi specs in a Crusader. Hell just take a fired case and put a bullet in it and chamber it then work the bolt back up and down and you should get a ring on the bullet and that will tell you where your at in relationship to the lands. Just a thought....