Anyone own a 7mm 300 Win Mag?

[Broz]

Com on Tres, you know the rules.... Post em up!

Jeff

 

[tresmon]

No groups really yet. I got it shooting about .35 moa @ 200 yards, but thats short range. I just got the barrel machined & on monday. Load development has just begun.

However I'm currently @ Rock Castle shooting center for a Long range steel shoot.
I have already found that pounding an IPSC sized steel target at 1120 yards in a shifty wind is a lot easier with 7mm pointed 180 Berger Hybrids @ 3100 than it was with 30 cal 210 vld's @ 2900.

We got a 16" plate up @ 1580yards I'll be giving a try tomorrow.

I'm sorry about the pics guys- All I have is a cell phone cam but I will try to get something up when I get back home...

 

[tresmon]

I still don't have a proper camera, but I did upgrade my cell phone today- it seems to have a really decent camera in it so I'll get some pictures up of my poor boy special.

Mean while get this-

.270-7mm-300Win mag!!!!!!!!
.270-7mm-300 Winchester Magnum! - Sniper's Hide Forums

 

[SidTheKidd]

Wow, a 1-18 twist huh? Sucky

 

[Broz]

How did you end up with an 18 twist barrel. I have never heard of one in .284?

I dn't know about running .277's down a .284 something about this process dosen't set well with my better judgment Tres. Be careful.

Jeff

 

[Weaselthis]

Well, it's NOT boring is it? LOL. Care to share some starting/stopping loads that you fire formed and final loads? I have a few more range days before I report on my new toy and am really enjoying the discourse from you and others on this subject. Be careful, dude.

I still don't have a proper camera, but I did upgrade my cell phone today- it seems to have a really decent camera in it so I'll get some pictures up of my poor boy special.

Mean while get this-

.270-7mm-300Win mag!!!!!!!!
.270-7mm-300 Winchester Magnum! - Sniper's Hide Forums

 

[Weaselthis]

OK, so I've had a little fun w/ this new toy and some consternation. Please let me run some data past you guys and get your feedback if you're bored and ya don't have anything better to do tonite!

So, my bbl. Is a Rem 26" take off 7mmRM reamed out using a 7m/300 reamer. Hey, $50 bbl. is perfect to experiment with!

I'm using Nosler custom 300WM brass necked to .284 w/ RCBS 7mmRM neck die and a little lube to "JUST" size tghe neck just above the shoulder and not crush anything. Case head measuremet just above the belt is VERY consistent at (.5095-.5100).

Worked GREAT for the first 50 fireform loads w/ 154g Hornady bullets, 70 H-4350 and Fed GM 215 primers (about 3204fps ave. & 142ES and no great shakes on accuracy,but again it's a $50bbl.). Bullet seated to cannelure which is WAAY off the lands….. ( .1340 off as I measure it w/ the Hornaday COAL gauge). No pressure problems.

Also, worked up a load w/ 180g Bergers, (.0165 off the lands) using the FF cases and 78 g H-1000 to get to 3014fps ave. f/ 3 shots that went into .9moa at 200yds. w/ no pressure signs. Good enough for me for killing things!

THEN, ran out of H4350 and hadda use H4831sc for the second fireform session of 100 cases. Hodgdon manual (circa 1985) for 300WM and 165g bullets indicate a range of 75.5g-81g and for a 150g bullet, 76.5g -82g of H4831. Since I'm using a 154g bullet, 77g outta be okay, right? Wrong.

Blew two primers completely out of the case. Fired 8 more w/ no blown primers but noticeable ejector marks on the case head AND…..case head measurements JUST above the belt indicate .5165-5.175. Check the all the other FF loads and THEY measure .516-.517 at the case head as well.

So, had a chamber cast made in IT measures .5165 just above the belt. This is 6-7 thousandths case head expansion! I was always lead to believe that .001-.003 was SOP. Input?

This weekend I ran 3 rounds thru w/ 75g H4831sc and the 154g Hornady. No blown primers, but still, the extractor mark is VERY visable. Extraction OK, but case head still measures .517 or so.

I had some of the "upper tier 78g H-1000" 180g loads using the previously FF cases and they all went bang without any issue. Seems like once you get it fireformed, it's okay.

BUT is there a "kaboom" in my future cuz I'm blowing the cases out way to far w/ this chamber/brass combo, weakening the case head web and cruising for a bruising?

All my data indicates that a 300WM is .511-.513 at the belt anyway for SAAMI specs. Given that, even THEY would expand to .0035 or .0055 in this chamber.

Whaddya think? Any help would be GREATLY appreciated.

 

[SidTheKidd]

I know that 77grn of H1000 is pretty hot for my 7-300 using 180 bergers.

I will measure my cases on my fire formed rounds to see what they are. I did measure them once and though I was right around .513 just above the belt. I had to do this because the cases were sticking in the chamber. Even when I had the load backed way way down.

 

[Weaselthis]

Thanks, Sid.
I worked up in 1/2g increments CAREFULLY measured, to 78g, because, as in the past w/ most of my Remmies, I could ususally be ok w/ slightly higher than max listed loads. Since all I have to go by is what this thread offers, I was careful in gettin there! No extraction problems, no pressure signs, ie, flat primer, ejector marks etc., and acceptable hunting accuracy for a factory take off bbl. BUT since this chamber is so large, I don't have a reference for head expansion that I go by. Only had problems (knock on wood, so far) w/ the second FF load and H4837sc which MUST be too hot cuz the primers came out! I don't care what the books say, if a primer comes out, SOMETHING is wrong in the mix! Usually it's the powder charge, IMO. But not sure here cuz it's uncharted territory for me.

If your cases come out .513 that would make sense, IF the virgin brass was .510-.511 to begin with. Couple thousandths expansion is acceptable, right?

I know that 77grn of H1000 is pretty hot for my 7-300 using 180 bergers.

I will measure my cases on my fire formed rounds to see what they are. I did measure them once and though I was right around .513 just above the belt. I had to do this because the cases were sticking in the chamber. Even when I had the load backed way way down.

 

[tresmon]

I had brass (given to me as once fired) sticking in the chamber too. I got a RCBS small base resize die and that cured it.

I got a 18 twist 7mm barrel this way:
crazy barrel story - Sniper's Hide Forums

I fire formed the brass with the .270 bullets and it all went fine, safe and cases came out good. I was surprised the rifle had some kick to it... the undersized bullets must have been trying to make a gas seal anyway. I learned that in a survival pinch I can shoot .270's through my 7mm.

Per load data I have found I seem to be able to use straight .300WM data for my 7-300.
I just go off the data for the same bullet weight. No I don't just jump into it blindly and load hot- but I have had no problem starting with middle 300WM loads in my
"7mm Win Mag"

Thanks fellas.

 

[tresmon]

Weasel,

When I was just beginning to load for this cartridge I used 7mmRM max loads as a start load for my 7mm-300WM. That never even came close to given me trouble or pressure signs.

No that I have some experience with it under my belt I have found no issue using low to middle loads of the straight 300WM data in my 7mm-300WM with bullets of the same weight.

My MAX loads to date is:
(MY rifle, 30" barrel, tight neck chamber, in cool weather- upper 50's)

!80 grain bullet:
IMR 7828 75.5g 3261fps
H1000 79.4g 3225f/s
Retumbo 81g 3311f/s

As always temps are warmer now & your gun will be different, So drop way back off these charge weights and ease back up in small steps watching for pressure signs.

 

[Weaselthis]

Tresmon, I read that Hide article. Good stuff! lol

Ya know, I used the 300WM data as well but got caught w/ my pants down!
IF my chamber has been reamed too large (and I have NO IDEA what specs SHOULD be, but have asked the smith who did the work to check into it for me) then I don't think I'll have a problem rezing them to fit w/ a regular die. Small base would be going in the wrong direction there, it would seem to me. Besides, I neck size only and don't usually FLS until absolutely necessary and then only bumb the shoulder back .002.

Really, the only thing so far that has me spooked is the amount of expansion to to fit the chamber here. I can pay attention to detail all I can, but if it's too big, no telling WHEN a particular piece of brass might let go! Ooopses are not my cup of tea. Thanks for the input. It's valued.
Take care.

I had brass (given to me as once fired) sticking in the chamber too. I got a RCBS small base resize die and that cured it.

I got a 18 twist 7mm barrel this way:
crazy barrel story - Sniper's Hide Forums

I fire formed the brass with the .270 bullets and it all went fine, safe and cases came out good. I was surprised the rifle had some kick to it... the undersized bullets must have been trying to make a gas seal anyway. I learned that in a survival pinch I can shoot .270's through my 7mm.

Per load data I have found I seem to be able to use straight .300WM data for my 7-300.
I just go off the data for the same bullet weight. No I don't just jump into it blindly and load hot- but I have had no problem starting with middle 300WM loads in my
"7mm Win Mag"

Thanks fellas.

 

[SidTheKidd]

You got those bullets flying out of there!!

Weasel,

When I was just beginning to load for this cartridge I used 7mmRM max loads as a start load for my 7mm-300WM. That never even came close to given me trouble or pressure signs.

No that I have some experience with it under my belt I have found no issue using low to middle loads of the straight 300WM data in my 7mm-300WM with bullets of the same weight.

My MAX loads to date is:
(MY rifle, 30" barrel, tight neck chamber, in cool weather- upper 50's)

!80 grain bullet:
IMR 7828 75.5g 3261fps
H1000 79.4g 3225f/s
Retumbo 81g 3311f/s

As always temps are warmer now & your gun will be different, So drop way back off these charge weights and ease back up in small steps watching for pressure signs.

 

[SidTheKidd]

Just measured the brass and it was was about .512 just above the belt. This was brass that has been fireformed in my rifle. Most were right there.

Thanks, Sid.
I worked up in 1/2g increments CAREFULLY measured, to 78g, because, as in the past w/ most of my Remmies, I could ususally be ok w/ slightly higher than max listed loads. Since all I have to go by is what this thread offers, I was careful in gettin there! No extraction problems, no pressure signs, ie, flat primer, ejector marks etc., and acceptable hunting accuracy for a factory take off bbl. BUT since this chamber is so large, I don't have a reference for head expansion that I go by. Only had problems (knock on wood, so far) w/ the second FF load and H4837sc which MUST be too hot cuz the primers came out! I don't care what the books say, if a primer comes out, SOMETHING is wrong in the mix! Usually it's the powder charge, IMO. But not sure here cuz it's uncharted territory for me.

If your cases come out .513 that would make sense, IF the virgin brass was .510-.511 to begin with. Couple thousandths expansion is acceptable, right?