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300 RUM Early Pressure Signs?

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Unread 09-29-2009, 12:37 AM
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Location: South of Canada and North of Wyoming
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300 RUM Early Pressure Signs?

Been working up some loads the last couple of days and I've been getting pressure signs kind of early.

Factory Sendero, Rem virgin brass, Fed GM215M

The following powder charges show pressure signs, stiff bolt, flattened and cratered primers, and extractor marks in all cases.

180 E-Tip, 98 gr Retumbo, Hodgdon recommended Max for 180 SPR SPBT bullets 100.5 gr
180 E-Tip 94 gr H1000, Hodgdoon recommended for 180 SPR SPBT 96, Nosler recommended max, 96 gr
200 AB, 92.5 gr Retumbo, Hodgdon recommended max 95.5 gr
200 AB, 91.5 gr H1000, Hodgdon recommended max 92.5 gr

The E-Tips were fired Saturday and it was warm out, about 75-80. The E-Tips are seated with a COAL of 3.69. ~.070 off the lands.

At 97.5 gr, the 180 E-Tip showed a whopping 3514 fps on the chrony in what appeared to be good light. I was stunned. The next load, 98.0 gr, was the pressure load and showed 3340 fps. The shadow of the range leanto had covered the chrony and when that happens, usually get questionable readings.

A 6 shot factory group of Winchester 180 Scirocco Bonded, Power level III registered an average speed of 3357 on Sat morn, which if corrected for chrony distance from the muzzles, works out to be 3367 fps, EDIT- Remmington shows 3250 fpr this load.

Last, I was also breaking the barrel in with Gun Juice... clean the bore of all copper, remover cleaner, apply a thin wet layer of Gun Juice, then fire a round.

The AB's were fired today at about 60-70 and seated with a COAL of 3.69, ~.100 off the lands.

I've read a lot of reports of guys using 95 gr of Retumbo with 200 AB's and no pressure signs. Any ideas why the early pressure signs?

Maybe some of the "hot" Hogdon powder???

Tomorrow the 210 Bergers get a try with Retumbo.



Last edited by MontanaRifleman; 09-29-2009 at 01:54 AM.
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Unread 09-30-2009, 09:05 PM
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Re: 300 RUM Early Pressure Signs?

Bringing this back to the top to see if someone might have some insight or similar experience?
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Unread 09-30-2009, 10:58 PM
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Re: 300 RUM Early Pressure Signs?

I noticed that when treating the bore with Gun Juice (leaving it wet as you're supposed to), my 'normal' load showed substantially increased pressure signs and slower velocities. I surmised that it might be from the wet barrel during the initial Gun Juice application process. Seems that might be a bit of a bore obstruction, in a way. Just my musing to try and explain what I saw. Perhaps a reduced load would be in order during the application period? Good luck. Jon
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Unread 09-30-2009, 11:35 PM
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Join Date: Sep 2009
Location: New Zealand (Tuakau)
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Re: 300 RUM Early Pressure Signs?

Tight chamber?? Velocity= preasure so if the speed is there for less powder you must have a near match chamber

I am using 92.2gr of ADI 2217 (H1000) for the 208 amax pills and getting 3200fps on a warm day
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Unread 09-30-2009, 11:41 PM
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Re: 300 RUM Early Pressure Signs?

Jon, I was wondering if that might be the case. I'll be finished with the break-in soon and re-fire those loads and work up again.

Leathal, being a factory barreled Sendero, I dont thimk it's a tight chamber. Thanks for the input.

We'll see what happens after the break-in is done.

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Unread 10-01-2009, 10:12 PM
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Join Date: Dec 2008
Location: rathdrum, id.
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Re: 300 RUM Early Pressure Signs?

Mt. rifleman....I've had two custom 300 ultras, one with a three grove 11 twist and one with a 6 grove 10 twist and both would shoot the recommended max no problem. With what you have said, I think the first thing I would try is a different lot of retumbo. By the way, if you REALLY want to get some velocity, get some T870 from thunderbird cartridge co. in Az. It's the same as the old H870 and if you have more than a 27" barrel I can just about guarantee at least a 100' increase over Retumbo. Good Luck......Ricjh
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Unread 10-06-2009, 07:19 AM
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Join Date: Aug 2007
Location: bismarck ND
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Re: 300 RUM Early Pressure Signs?

i have the same thing going. i shoot a ssg custom 300 ultra i had to back my retumbo load down to 89.5 grains which is 3 grains under the starting point in alot of the manuals. this rifle will shoot 1/4moa. if you search my posts you will see alot of my pictures. i have found that i am getting all of the velocity that the guys are getting useing more powder.
load 89.5 retumbo 215m primer 210 berger oal 3.770 with stoney point gauge 3070fps i have tested this load with 60 rounds all 600 and 1000 and it shoots extremly well.
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