Seating dearth and pressure

[Ttocs]

Just a quick question for the experts.
I’ve been very lucky with my load development for all my rifles but for my 17 REM. Usually I find a powder charge that gives a 1 hole group with similar results when looking at charge weights either side. I found a reasonable group 1”, with similar groups either side, for the 17 but would like to reduce this.
So my next plan is to fiddle with the seating depth; I’m thinking several .005” steps either side of my current c.o.a.l.
My question, clearly moving the bullet and increasing/decreasing the volume of the cartridge will affect pressure, but how much? Could it be enough to cause a spike in pressure?
Cheers
N

 

[Lateral]

Increasing the seating depth/increasing the jump to the lands, often "reduces" pressure, because the longer jump allows the bullet to engage the lands at speed, overcoming it jamming so hard

 

[Ttocs]

My tiny little bullets have an almost .2” jump to the lands ( yes 5mm) from SAAMI spec.; if I have a minimum seating depth equal to the bullet diameter I can’t get anywhere near the lands. I think I’m just playing with case volume by adjusting the seating depth.
N

 

[Ade8mm]

Isn't that what train commuters used to suffer before the bat flue?

 

[Border]

Just a quick question for the experts.
I’ve been very lucky with my load development for all my rifles but for my 17 REM. Usually I find a powder charge that gives a 1 hole group with similar results when looking at charge weights either side. I found a reasonable group 1”, with similar groups either side, for the 17 but would like to reduce this.
So my next plan is to fiddle with the seating depth; I’m thinking several .005” steps either side of my current c.o.a.l.
My question, clearly moving the bullet and increasing/decreasing the volume of the cartridge will affect pressure, but how much? Could it be enough to cause a spike in pressure?
Cheers
N

Depends on how hot your load is to start with. I 've not had to experiment with seating depth to get my 17 Rem to shoot bugholes, just standard c.o.a.l.

 

[stubear]

How long are you loading now?

Personally I just load to SAAMI max OAL and be done with it, so I dont really have much option to lengthen things further in any case!

 

[Milligan]

the impact length has on pressure and velocity depends where you are on the curve, it's not a straight line relationship.
In many cases moving about is fine, in others shortening a load by just a little can go from ok to stiff bolt and flat primers.
chrono is always useful as is staying in the realms of published data.

 

[Selous]

I found the 17 REM to be an interesting cartridge to load and it is the one that came closest to kicking my butt with a rapid pressure spike. One thing I would advise is to start load testing with a very clean barrel. My rifle does about 50 rounds then opens up. I use an abrasive cleaning paste every time on my 17

 

[Milligan]

I found the 17 REM to be an interesting cartridge to load and it is the one that came closest to kicking my butt with a rapid pressure spike. One thing I would advise is to start load testing with a very clean barrel. My rifle does about 50 rounds then opens up. I use an abrasive cleaning paste every time on my 17

you hoping to make it a 19 Rem soon?

 

[Ttocs]

Thanks for the replies. I’ve had the rifle for 3 years now and after nearly 300 rounds of development (latest 40 rounds was with a barrel tuner) I’m not getting the groups I’d like.

My current load has:
a coal of 2.154” (SAAMI 2.150” & Nosler data 2.140”) not quite sure how I ended up at 2.154
23.8gr N135
Rem 71/2 primer
Rem case
20gr Nosler Varmageddon

I’m thinking time for a change of barrel if seating depth doesn’t pull things together (perhaps even if it works)