300 RUM Early Pressure Signs?

[MontanaRifleman]

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.

Thanks,

-MR

 

[MontanaRifleman]

Bringing this back to the top to see if someone might have some insight or similar experience?

 

[jmden]

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

 

[Leathel]

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

 

[MontanaRifleman]

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.

Mark

 

[elkaholic]

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

 

[tjonh2001]

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.

 

[MontanaRifleman]

Thanks for all the input guys. I really appreciate it.

I am certain it's the Gun Juice treatment. This morning I took some 25-06 loads to the range with my300 too. I applied some gun juice to the bore for the first round and got a real stiff bolt and blew the primer. This is a load that I had fired several times with no previous pressure signs. I fired some other low charge, work up rounds through it and then came fired the same load that blew the primer. No pressure signs this time.

I had applied some GJ to the bore of the 300 the night before and went to fire a string of 180 E-Tips I had loaded with Retumbo, at the charge that had not given me pressure signs. I got a very stiff bolt, extractor mark, and cratered primer. I cleaned the bore, tried a couple of other loads through it and them went back to the E-Tips with Retumbo. No more pressure signs. Good velocity, about 3430.

Lesson learned… don't shoot warm or near max loads through a bore that has fresh GJ applied to it. Including warm factory rounds like Rem Power Level III for 300 RUM. Got some pressure signs from them too during the break-in process.

Thanks again guys.

-MR

 

[MontanaRifleman]

Update:

I took these loads out to the range again today and her are the results...

180 E-Tip, pressure signs at 98.5 gr of Retumbo. No signs at 98 gr with 3440 fps.

180 E-Tip, ran through my string up to and including 98 gr of H1000. No pressure signs. 3400 Plus.

200 AB, ran through my string up to and including 97 gr of Retumbo. No pressure signs. 3270 fps.

200 AB, ran through my string up to and including 94 gr of H1000. No pressure signs. Less than 3200 fps, it was overcast and getting dark.

210 Bergers, ran through my string up to and including 93 gr of Retumbo. No pressure signs. 3130 fps.

Got some really good velocities, My chrony was in the shade most of the time and intermitant sun and clouds. Usually low light means low readings in my chrony... but hard to say. Will being going back for more load development and chrony readings, hopefully on a better light day.

So it seems the early pressure signs wer due the the Gun Juice treatment, and possibly also high velocities today.

-MR

 

[Leathel]

all looks good

I should have another 300Rum up in running in a couple of weeks with a slower twist to try some lighter pills...Might load 150's-180's so will be interesting to see where the preasure is in that compared to the 1:10 factory sendero barrel (mine was 300wm reamed to 300 Rum)


(actualy had a 28" Shilen Taget 308 barrel with a 1:12/13 twist will measure the twist soon)