7mm practical help please

[Jakeleg]

Hi everyone,I have a question for the 7mm-300 and 7mm practical crowd,I have a 28 inch Krieger HV 1-8 twist and we chambered it to the 7mm Practical Revision B reamer,brand new reamer but we throated it for 195 bergers. My length to lands is 4.080 and have been shooting the bergers anywhere from 4.070 to 4.000 to ogive measured with hornady comparator. My question is I get some serious pressure signs like my brass almost always gets a ejector flow and sometimes leaky primers and the belt expands around .005 primer pockets seem to get loose on first firing. I had it chambered for same round but we rented a reamer and was having problems with what we thought was sloppy chamber but with new reamer it and long throat I can't get what I think I should anyhow.I have used old stock ww brass,new ww brass,rem brass and hornady all with same results. The rifle shoots bugholes but even with 74 grains or reloader 33 with 195s or 70 grains of H1000 it still gets loose primers and ejector marks like a good solid bump. I am stumped. I thought we had too much headspace so I had him cut it back to almost none and although the rifle shoots lights out the brass is basically junk after a couple firings. Any thoughts would my long throat cause pressure signs?It seems the chamber is nice and tight,I've tried different primers,H1000 Retumbo and R33.All these loads are way less than I shot out of previous chambering with the rented reamer. I am lost,I know I could have a tight bore but I even tried some 168 grainers and 180 with lower charges and still get the loose primers and ejector hole mark. Thanks in advance

 

[elkaholic]

Have you chronographed it?

 

[FEENIX]

Hi everyone,I have a question for the 7mm-300 and 7mm practical crowd,I have a 28 inch Krieger HV 1-8 twist and we chambered it to the 7mm Practical Revision B reamer,brand new reamer but we throated it for 195 bergers. My length to lands is 4.080 and have been shooting the bergers anywhere from 4.070 to 4.000 to ogive measured with hornady comparator. My question is I get some serious pressure signs like my brass almost always gets a ejector flow and sometimes leaky primers and the belt expands around .005 primer pockets seem to get loose on first firing. I had it chambered for same round but we rented a reamer and was having problems with what we thought was sloppy chamber but with new reamer it and long throat I can't get what I think I should anyhow.I have used old stock ww brass,new ww brass,rem brass and hornady all with same results. The rifle shoots bugholes but even with 74 grains or reloader 33 with 195s or 70 grains of H1000 it still gets loose primers and ejector marks like a good solid bump. I am stumped. I thought we had too much headspace so I had him cut it back to almost none and although the rifle shoots lights out the brass is basically junk after a couple firings. Any thoughts would my long throat cause pressure signs?It seems the chamber is nice and tight,I've tried different primers,H1000 Retumbo and R33.All these loads are way less than I shot out of previous chambering with the rented reamer. I am lost,I know I could have a tight bore but I even tried some 168 grainers and 180 with lower charges and still get the loose primers and ejector hole mark. Thanks in advance

lightbulbWOW, that's some serious CBTO ... even for a COAL!lightbulb

I know the 195s (1.648") are long but not that long; in comparison here's my .300 WM with 200 NAB (1.490") ...

(CBTO)

(Zeroed with Hornady LNL comparator)

(COAL)

 

[Wachsmann]

That's even longer than my RUM to the lands if my memory is correct.

 

[ksubuck]

Something doesn't make sense to me. Case length should be 2.620 plus a bit for the practical as the case stretches a bit over time, and bullet length 1.648. The combined length would be 4.248 if you didn't seat the bullet at all. To account for boat tail and neck length when seated, I would think the longest OAL you would see could be around 3.750 and some change. The CBTO would obviously be less than that. Any chance you aren't zeroing your calipers when you put your comparator in? That would make your CBTO numbers 3.000 to 3.070 which still seem too long.

Are you sure that you aren't significantly jammed into the lands??? It can be difficult to feel the lands when checking with the Hornady/Stoney Point setup.

Useable case capacity on this round would be 84ish grains H2O. Why not seat that puppy deeper and jump it some? VLDs do jump in many cases. Might help with the pressure symptoms some? Recheck, and recheck your lead. How much freebore did you put in?

I put 0.200 in my 7-300. From the bolt face to the lands is 2.893 inches. My COAL is 3.605 and CBTO 2.805 with the 180 VLD.

Also, did you use a reamer with the throat cut included or did you use a second throater after reaming the chamber. A Revision B reamer from PTG is a zero freebore reamer. Check that as well. You may not have a throat.

 

[AZShooter]

I agree with ksubuck, you might be into the lands. An easy way to SEE is to polish the jacket with fine steel wool then chamber the round. If it is contacting the rifling you will see evenly spaced rectangular or square marks on the jacket.

The creator of this round,

7mm Practical

states load data of 71-74 grains of h1000 for the 190 gr bullet. No mention of the heavier 195 berger. Perhaps your load of 70 gr of h1000 is just too much for this bullet? Have you tried lower powder charges? It sure sounds like you are way over the top with the powder charges.


I too want to hear what you are getting for velocity.

 

[CogburnR]

I'm guessing that the cbto is without the comparator subtracted. I have the 270/300wm and my cbto to lands is 3.95" without subtracting the comparator.

If you are getting that much expansion and killing brass there is pressure.

My guess is that the reamer is a tight neck version and you may need to neck turn the brass for clearance. Check the reamer print is available for the neck dimension and allow for min. neck clearance on loaded rounds. I ran into this kind of thing when the brass needed to be trimmed also. The chamber was basically crimping the bullet in place resulting in pressure.

 

[Jakeleg]

Thanks guys and cogburn,that is what I was suspecting it could be crimping the bullet and sorry that measurement is without zeroing on the comparator I will look a little more into neck area. I didn't plan on throating quite as far as we did but as it turns out it works really good for length of 195s or it would if I could fill her on up with powder now, thanks

 

[Jakeleg]

And yes we did use separate reamer for throating and went a little farther than I planned ended up at 3.080 to the lands (with the comparator subtracted sorry) and the only reason I thought it was a light enough charge is going by past experience with my old chamber and trying 70 grains of h1000 and retumbo with the 180s I still get the same pressure signs.i am going to check the neck area and will report back I am getting a straight 3000 fps with the 75 grains r33 and the 195 and can live with that if I can keep primers in thanks

 

[ksubuck]

Good deal, sounds like the throat probably isn't the problem. Let us know about the neck as it would be the next most likely problem. Do the rounds chamber easy?

Are you using new brass or brass from your previous rifle?

What was your previous barrel?

 

[Jakeleg]

New brass and this is same barrel just rechambered it and set it back as it only had 250 rounds on it but I have a krieger light varmint 1-8 barrel to build another but now I'm thinking maybe I should retool and give a 28 nosler a try it's just I have all the dies and plenty of 300 mag brass I was hoping to get this panned out not really wanting to shoot anything lighter than 180s and 195s I have a 7mm mag for that. Thanks

 

[Dolphin]

Hi everyone,I have a question for the 7mm-300 and 7mm practical crowd,I have a 28 inch Krieger HV 1-8 twist and we chambered it to the 7mm Practical Revision B reamer,brand new reamer but we throated it for 195 bergers. My length to lands is 4.080 and have been shooting the bergers anywhere from 4.070 to 4.000 to ogive measured with hornady comparator. My question is I get some serious pressure signs like my brass almost always gets a ejector flow and sometimes leaky primers and the belt expands around .005 primer pockets seem to get loose on first firing. I had it chambered for same round but we rented a reamer and was having problems with what we thought was sloppy chamber but with new reamer it and long throat I can't get what I think I should anyhow.I have used old stock ww brass,new ww brass,rem brass and hornady all with same results. The rifle shoots bugholes but even with 74 grains or reloader 33 with 195s or 70 grains of H1000 it still gets loose primers and ejector marks like a good solid bump. I am stumped. I thought we had too much headspace so I had him cut it back to almost none and although the rifle shoots lights out the brass is basically junk after a couple firings. Any thoughts would my long throat cause pressure signs?It seems the chamber is nice and tight,I've tried different primers,H1000 Retumbo and R33.All these loads are way less than I shot out of previous chambering with the rented reamer. I am lost,I know I could have a tight bore but I even tried some 168 grainers and 180 with lower charges and still get the loose primers and ejector hole mark. Thanks in advance

New brass and this is same barrel just rechambered it and set it back as it only had 250 rounds on it but I have a krieger light varmint 1-8 barrel to build another but now I'm thinking maybe I should retool and give a 28 nosler a try it's just I have all the dies and plenty of 300 mag brass I was hoping to get this panned out not really wanting to shoot anything lighter than 180s and 195s I have a 7mm mag for that. Thanks

 

[lancetkenyon]

2.5+ year old thread.....nice bump.