Where Did My Wildcat Plans Go Wrong

[Rockdoc173]

Since the 6.5 PRC came out, I have wanted to neck it up to 7 and make a 7mm-08 big brother in a SA. I finally got all the components assembled and sent them to the gunsmith. After two years of plotting and planning, I fired the first rounds last week. The results are encouraging thus far, however it's not without some measure of disappointment and I am now trying to understand what I did wrong. When Manson drew my reamer, it was with the understanding that the COAL had to be <2.95, so SA. We started with a SAAMI 6.5 PRC print, blew out the mouth to accommodate the 7mm, and cut the freebore down to a short 0.045. In my mind, I was wanting to get a COAL in the 2.96 region so I could have ~0.010 jump at mag length. Instead, the 166 ATip sits at a CBTO/COAL of 2.477 / 3.170, the 168 VLD at 2.478 / 3.158, and the 180 Hybrid (what we designed the cartridge for) at 2.521 / 3.208. This produces jump values of 0.22, 0.208, and 0.258 respectively. Clearly I "missed the target." The gun seems to be shooting, but I'm more concerned with why this happened. How does one reconcile the COAL / jump / target length relationship so that proper planning can be achieved? My next wildcat will likely be something like a 7mm 30cal magnum (PRC, WM, etc.) where an extra 1/4" could hurt me in terms of the overall usability of the rifle.

Would making a dummy round and sending it to the reamer manufacturer be the more reliable way of doing this? It would be using virgin brass, but it seems that would be more effective than going the reamer print > die > brass direction

 

[ShtrRdy]

I think I would talk to the Reamer manufacturer to see where the process went wrong and how it could be improved.

 

[RegionRat]

When someone designs a reamer in Wildcat territory... with respect to bullets and barrels, there is no way to anticipate the bullet touch point since they don't have your barrel or a huge experience base behind them. They can and often do come close.

Even providing a dummy bullet leaves a risk that your specific barrel has differences in lands and grooves that change the seating depth issues.

Providing a gunsmith with a throating reamer and a dummy round is one way to avoid surprises. Eventually through trial and error a recipe for the bullet/barrel/reamer can be achieved, but it usually takes a few tries. YMMV

ETA, very nice rig.

 

[CaptNemo]

I know what's wrong with it...
They put the bolt handle on the wrong side of the action.

 

[whatsupdoc]

The Fclass guys use the 284 Shehane with a .225 throat for 180 Hybrids, many run .010 or more
jammed into the lands. You should of started researching 7mm throat/bullet combos not just
randomly reducing a 6.5mm throat.

I would search for what COALS they are using for the 284 Shehane or 284 Win its parent cartridge and
you could see what number would have worked.

At this point I would just load to whatever shoors good and single load if necessary.

 

[Rockdoc173]

Hater…lol

 

[The D]

Are you shooting anywhere near sw FL? Can I come shoot and help with data gathering? I’m here visiting the in-laws and need a break

Sorry for the temporary derail

 

[TheOfficeT-Rex]

Sounds like with that bullet and lead angle, you were not going to get to touch even with a zero freebore.

It's good advice to look at the fclass and BR guys reamer designs, just remember that they all single load so there's more leeway for design and length for loading into/at the lands.

 

[CaptNemo]

Hater…lol

Plumber... In my experience, there is a far higher concentration of southpaws in the plumbing trade than probably any other field.

Come hang out in the Bear Pit and see that I learned from the best Haters on this site...
I am but a Padawan Learner amongst Jedi Masters.

 

[Ledzep]

Not computing how you jump .258" with .045" freebore.

ETA: Was the reamer accidentally made with 0.45" freebore?

 

[Travis224]

Can't you have the reamer reground? I've ordered stock reamers and had it shortened by Manson (creedmoors in 6mm and 22 for varmint bullets). You'd have to set the barrel back 2 threads which is, what I'm told, is standard. Or, just see if it shoots to your liking as is and don't worry about it.

I understand you want to understand what happened, I wouldn't fret too much if it shoots the way you want.

Currently I have 15ish barrels for my TL3s, and only 4 are SAAMI cartridges.

 

[Rockdoc173]

Quick little update on this topic.

The modified case I am using is a Hornady case with the mouth pushed out to 7mm. I used a 0.284 mandrel to expand it, but it wasn't enough to allow the bullet to slide easily. My buddy made me a 0.288 and it worked fine except that I had trouble getting it out resulting in a slightly oversize mouth. This oversize allowed the bullet to move around a bit, but it was enough to get me in the ball park. Fast forward to yesterday, I was going to load 180s all the way out and discovered that "all the way out" is only about 0.05 past the the mag. The variation I got in the modified case masked the much shortened reality so in the end it actually worked out quite well.

 

[2aBaC̶a̶]

are you by chance an engineer?

 

[Rockdoc173]

are you by chance an engineer?

not hardly. lol

 

[Mike Casselton]

@Rockdoc173 myself and @Schütze shot together yesterday.
I'd have to say that the rifle, and the shooter do just fine.

I replicated Rockdoc's impacts from yesterday by drawing them in on this image in a bluish-black color.

(The picture was taken when we drove out to pick up a privately owned camera. We weren't able to drive back out there after Rockdoc was done shooting)

The two actual bullet impacts from other shooters are as follows:
The low, left was an accidental hit by someone that was shooting at a 36"×48" target to the left of the IPSC.
The high belly button shot that barely broke the outer layer of paint was from a 6-BR/105.

Anyway, this is a standard IPSC at a mile.
First impact low along the bottom. Corrected hold and then 4 consecutive impacts just left of center. All circled in green.


I'm thinking he'll do okay once he settles on a load...