Which is best, parallel or standard SAMI spec tapered leade

[diditg]

Right, I've finally decided to build a new 7mm-08, to which end I've acquired a Sako 75 stainless actioned rifle to use as a donor.

In the past when talking to various gunsmiths about chambering a new barrel, some have said that their preference was to use a reamer which gave a parallel leade, as opposed to a standard SAMI spec tapered one ( might have got the terminology slightly wrong here but hope some one knows what I'm on about)

From these conversations and what research I've managed to do, it appears that the advantage of a parallel leade is that the rifle is less fussy about bullets of differing weights, lengths and seating depth.

To any of the members who have experience of this or have rifles chambered thus, what are their thoughts / experiences. Are there any disadvantages?

My current 7mm-08 has a 21 1/2" barrel, is there an optimum length when using120gn and 140gn ballistic tips?

[Scotch_egg]

I am sure one of the resident rifle builders will be along to comment on chamber spec.

 

As for barrel length I use a 19" 7-08 and shoot 140gr Noslers exclusively because they work on everything from fox to big reds. I achieve 2725fps with varget.

 

If I was building my rifle again I would look at using 120gr TTSX out of a 16" barrel after seeing an article from New Zealand.

[Laurie]

I think this may refer to the throat angle. Remy tends to use 3-deg or even a little more on all its hunting cartridge chamber specs, whilst half that is regarded as a 'good thing' in most match rifles, and .308 Win has 1 1/2-deg as the SAAMI standard angle.

 

Dave Kiff's book of standard chamber drawings for gunsmith has three variants of off the shelf 7mm-08 Rem chamber designs.

 

7mm-08 Ackley Improved version: 0.2845" (parallel) leade; 0.2845 - 0.2730" throat; throat angle 2-deg (print # 115)

 

7mm-08 Remington: 0.2845" (parallel) leade; 0.2845 - 0.2720" throat; throat angle 3-deg (print # 202)

 

7mm/08 REM MATCH: 0.2840" (parallel) leade; 0.2840 - 0.2720" throat; throat angle 1 -30-Deg (print #445)

[Chris-NZ]

Scotch is right- "Bush Pigs" in 7-08 or .308 are all the go here. Mainly built on T3s chopped right back so the can just clears the forend.

 

The secret is compensating for the short barrel with clever choice of components. The default 7-08 load (which mine shoots into ~2/3" 5 shots) uses H335 behind a 120TTSX and gives ~2940MV. Kills very well. The last nine shots I've fired have got seven deer- one of the extras was a miss on a trotting stag and the other an unnecessary finisher as it turned out. Three of the seven were over 300yds. Have only recovered one of these projectiles and that was found in the rump after shooting it front on 336yds away.

 

[diditg]

Hi Laurie,

Thanks for taking the time to dig that data out for me. I must admit I haven't had the sort of response I was expecting, I expected a few responses stating this works or that works but these are the compromises, however I suppose a lot of people out there will only know that their rifles been optimised to shoot a certain bullet length/type rather than the fine details of how the throats been configured

 

Hi Chris,

That's a purposeful looking bit of kit, am I correct in thinking that's a 16" barrel, if so what twist rate does it utilise. I suppose the other question I should ask, if you don't mind divulging, is what coal does it utilise with the 120gn ttsx and what jump does that give.

[baldie]

Bear in mind that after the first 100 rounds down it, it wont matter a jot what leade angle was used.

 

My 7-08 reamer is std SAAMI spec as per Dave Kiff and it has produced 1" groups at 400 yards in two different rifles.

 

People worry far too much about such things. Std reamers are set up to shoot an optimum bullet weight range for that cartridge, and work perfectly.

 

Dont try to fix what ain't broke.

[Chris-NZ]

Diditg-

 

it's a std 9.5 twist Tikka barrel chopped to 16.5". The Gen 4 Hardy can clears the std forend by 5mm. As for the TTSX load, it's at max mag length of 2.83" which is still a fair jump but they shoot well.

 

The Bush Pigs are ideal for NZ conditions - compact for the thick bush and light enough to carry round our mountains. Guys that have a play with one often end up getting one themselves- three others have from mine alone. The article that Scotch alluded to was no doubt in the NZ Hunter magazine. The latest edition has a variation on it. Called the Superpig, it's a .284 version built on a T3 from a take-off 700 barrel. It drives 140gr E-Tips at 2900 using Re17 and was stonking accurate. They put a CF stock on it and with a 3.5-10 CDS Leupold on it, all-up weight was just over 6lbs. That's a helluva lot of firepower in a very compact package. His English-born wife nailed a chamois in the Southern Alps at over 400yds, the first animal to fall to it.

[Ronin]

I looked at leade angles a bit when trying to develop my own variation of the 7mm/270 I'm using in F Class.

 

1.5 degrees seems to be the norm with 1.0 degree being the shallower angle which in theory should develop less initial pressure and wear slower….

 

In theory.

 

Having done quite a bit of shooting using both and extruded (stick) powder - I can't honestly say I've noticed any difference in wear or accuracy.

 

If you are running a seriously over bore calibre - like say a 30 or 7mm/ 338 then the shallower the leade angle the better, but there are ways of reducing wear as well as this, such as using ball powder (which doesn't cut as much )- research proven by Kirby Allen and also improving the case, where the poser is funnelled to burn within the case neck rather than in the leade.

 

 

Id stick with whatever your gunsmith chooses (which will be probably a 1.5 degree taper) unless your making some Wildcat of a futuristic design that no one else has thought of...

[Chris-NZ]

I seem to recall my older gunsmiths saying shallow leade angles tended to shoot straight off, ie didn't need any running in to develop their full accuracy potential. But as Dave said, a few hundred rounds down the track, there's probably no difference

[bradders]

My own opinion is that none of it matters

[diditg]

Hi all

Thanks for all of your replies.

In some respects I've possibly answered my own question, Laurie's data got me thinking.

I realised that I'd made a mistake in that the original conversations I'd had with a gunsmith had been about . 270 Winchester and 280 Remington calibers, whereafter I'd decided to stick with 7-08. The extra velocity wasn't really necessary for the stalking ranges I shoot at and the extra barrel length required to get the best out of the 280 rem was going to be more of a disadvantage than the velocity gains were going to be an advantage.

Having discovered that chamber drawings are available to view on the SAMMI site, I've realised that a standard 7-08 chamber actually does have a parallel section of leade ( could this also be described as freebore) before it transits to a throat angle of three degrees, or in the case of some of the other variants as little as one degree.

All in all I suppose it was a bit of a non question really, however the responses have borne some interesting information.

So once again, thanks to those who have responded.

Diditg