338 Lapua Improved 40 degree with print. Which design is better?

[yorke-1]

The G and I specs are larger than all other .338 prints I've seen today. Most if not all are .3385. Isn't .3395 too large permitting excessive blow by as phorwath mentioned?

Possibly, but it's unlikely that it's going to make a huge difference. It will however allow for a little bit of wiggle room for loaded rounds with a bit more bullet runout or less than perfect concentricity. I have a few chamber which have a leade that's just .0005 over bullet diameter. If you get sloppy with your hand loads of have a dirty chamber you can have problems.

Andrew

 

[Pdvdh]

The G and I specs are larger than all other .338 prints I've seen today. Most if not all are .3385. Isn't .3395 too large permitting excessive blow by as phorwath mentioned?

Kirby Allen is one gunsmith that has discussed the tighter "LEAD" dimensions as beneficial. If you're looking to fine tune performance for long range accuracy and improve throat life, minimum tolerances can be beneficial. How much benefit is there? I haven't a clue how to quantify it. The gunsmiths that specialize in LRH and maximizing accuracy order 0.3385" diameter "LEAD"s for their .338s, as best as I can determine. If you're hunting elephant in their mud wallows, perhaps you'll forego some of the benefits and choose a looser chamber reamer.

 

[Despotes]

Kirby Allen is one gunsmith that has discussed the tighter "LEAD" dimensions as beneficial. If you're looking to fine tune performance for long range accuracy and improve throat life, minimum tolerances can be beneficial. How much benefit is there? I haven't a clue how to quantify it. The gunsmiths that specialize in LRH and maximizing accuracy order 0.3385" diameter "LEAD"s for their .338s, as best as I can determine. If you're hunting elephant in their mud wallows, perhaps you'll forego some of the benefits and choose a looser chamber reamer.

I'm not putting this together to hurl bricks at Dumbo. I want precision, like most people here.

 

[yorke-1]

I'm not putting this together to hurl bricks at Dumbo. I want precision, like most people here.

Don't give up on it yet. Some of my most accurate long (1400 yards and under) range barrels are cut with standard factory chambers. These are 19" mcgowen barrels on savage striker pistols in 284 win and 260 rem. both will hold .75 MOA or better right up until they go subsonic.

A different reamer won't make up for bad smith work or a bad barrel.

Andrew

 

[Despotes]

Changes made. Look better? Should I extend the throat (W) the same amount I did the lead?

 

[Pdvdh]

I'm not sure why your reamer spec sheet came with a larger dimension on the OD of the neck at the neck shoulder junction than at the case mouth. Question? Are you going to ouside neck turn your case necks?

I think the neck OD dimension "C" on your reamer spec sheet could/should be the same as dimension "H", 0.372", instead of 0.3744" & 0.37425". I went with 0.370" at both locations because I'll be truing up my case necks by outside case neck turning. Notice that the two reamer specs I added to your thread both use the same dimension of outside neck diameter at both locations of the neck - one at the shoulder joint and one at the case mouth.

The THROAT would basically increase the same amount as the increase in LEAD. Unless you decrease your outside neck diameter. Then the THROAT will be just an itsy bitsy bit less of an increase due to the decrease in outside neck diameter. Your reamer company should have a tech person that can talk to you and help you thru this also. I'm no expert. I figured out about what I wanted after determining a target COAL with my bullet of choice, and reviewing some other reamer spec sheets for reputable sources. I still relied on Dave Kiff (PTG) to ensure I wasn't making some sort of fatal error in my modified spec sheet. Dave talked with me once or twice briefly by phone.

 

[Despotes]

Updated again. As far as outside neck turning goes, Undecided. Pro's? Cons?

 

[Pdvdh]

If you outside neck turn to just barely clean up the neck, then 0.370" will be good for the neck OD. If not outside neck turning, you'll want to use 0.372" OD on the neck with factory Lapua cases.

Your shoulder OD dimension "E" of 0.570" is pushing it for case body taper. Nathan Dagley's reamer spec sheet used 0.569". I went with 0.562"diameter at the case shoulder. If you don't have enough taper to the casing from case head to case shoulder, case extraction can become difficult/problematic. So you could discuss this with your chamber reamer supplier, but I would reduce the 0.570" shoulder OD to something more like 0.565", to help ensure you don't have difficult case extraction problems.

 

[Edd]

I'm not sure why your reamer spec sheet came with a larger dimension on the OD of the neck at the neck shoulder junction than at the case mouth.

That is how you want it. The neck needs some taper just like the body needs some taper.

 

[Pdvdh]

That is how you want it. The neck needs some taper just like the body needs some taper.

I don't believe that's an issue if you outside neck turn the case necks to a uniform thickness. Perhaps it's correct if you're not outside neck turning. Look at the "Speedy" and "Nathan Dagley" spec sheets. Both of these gunsmiths are very experienced. The case neck will never offer enough resistance to cause difficult case extraction, in my opinion. Not enough surface area and length on the case neck to cause significant friction binding. The case body has much more surface area and length, so yes that can cause problems. That's my take on it.

Anyhow, Despotes - be sure to inform your chamber reamer manufacturer whether or not you intend to outside neck turn your cases or not. Then they'll know how to spec out the neck OD on the neck reamer. Dave Kiff (PTG) had some factory loaded .338 Lapua brass next to him when we talked on the phone. He placed his calipers on the OD of the necks on this loaded brass and provided me with the OD. I was thus able to confirm that 0.370" neck OD on my neck reamer would be good for outside neck turned brass. You want the chamber to be about 0.004" larger in diameter than the casing necks with the bullets seated in them.

It's no coincidence that Nathan Dagley spec'd the same neck OD on his neck reamer. I'm sure Nathan was planning on uniforming the necks on his brass, as I intend to do also. Speedy spec'd his neck OD at 0.371", both at the shoulder and at the case mouth.

 

[Edd]

I believe having a slight taper on the case neck is the correct way regardless of how many examples you can find of experienced people doing it the incorrect way.

 

[yorke-1]

I really believe that you're over thinking this. The reamer that you have in your hands will give you excellent velocities and be just as capable of hitting deer sized targets at pretty much any range that the cartridge and shooter are capable of making hits at. If you were planning to compete in bench rest matches it may make a difference, but not in a hunting gun.

Extending out the lead as far as you have it in the last print can cause premature throat erosion in addition to making it difficult to shoot some bullets seated to the lands. I'm always reluctant to design a chamber around one bullet. I've done it, but it was a gamble. What happens if that particular bullet just won't shoot for you? Then you may not be able to hang your second choice bullet out there far enough to find the sweet spot from the lands. Also consider that it will be difficult to adjust seating depth as the lands do start to erode if the bullets are already hanging out as far as they can.

Andrew

 

[Pdvdh]

I believe having a slight taper on the case neck is the correct way regardless of how many examples you can find of experienced people doing it the incorrect way.

Until you explain why slight taper in a case neck chamber is the correct way, and a constant case neck chamber diameter is the incorrect way, you won't have established anything but the expression of your opinion and belief system. I'm willing to be corrected, but not misguided. If you would like to present instruction, explain yourself. Why is a constant neck diameter in a chamber incorrect, particularly for those who outside neck turn their case necks?

Difficult case extraction isn't a plausible explanation. Otherwise Speedy, Nathan Dagley, and Dave Kiff from Pacific Tool & Gauge would have disappointed an awful lot of customers. I'm shooting a 30/375 Ruger Improved now with constant neck chamber diameter without any negative side affects. No difficult extraction.

 

[Pdvdh]

Extending out the lead as far as you have it in the last print can cause premature throat erosion...
Andrew

Not if you keep the LEAD restricted to 0.0005" over bullet diameter. Perhaps you'll experience additional throat erosion if you cut the LEAD 0.0015" over bullet diameter. The reason to go 0.0005" over bullet diameter is to prevent excess gas blowby, and to help ensure the bullet is precisely aligned with the bore as it enters the lands of the rifling. That's how it's been explained to me. And those explanations make sense.

I don't understand your reluctance to design a chamber and LEAD around a certain bullet when building a custom rifle. This member has already stated his intention of running 300gr Berger OTMs. That's a long bullet. Why wouldn't a guy lean toward a longer LEAD when intending to shoot one of the longest bullets manufactured in .338 caliber. Yes there's no guarantee the rifle will shoot the 300gr OTMs splendidly. Who's to know at the time of rifle design and construction. Sometimes the Bergers shoot well 0.010" off the lands. Sometimes they shoot better 0.080" off the lands. You'll never get 0.080" off the lands with a shortened LEAD without seating the bullet deep into the casing, needlessly consuming case capacity. If it won't shoot 300gr Berger OTMs, that doesn't mean it's to the scrap heap. Try the Sierra .338 300gr Match Kings or the Hornady .338 285gr A-Max, both of which are also long bullets. I surely didn't design my LEAD for 200-250gr .338 bullets for Long Range Hunting. I designed it for the higher BC (long) bullets in order to maximize retension of down range velocity and reduce wind drift at long ranges. If I wanted to proceed with a one-size fits all approach, I wouldn't have ordered a chamber reamer in the first place. Just go down to Walmart or Sportsman's Warehouse and order a factory rifle chambered in the standard .338 Lapua, designed to digest all factory ammo satisfactorily, and live with those average results. There's no guarantee it will shoot ANY bullet well, let alone the longest highest BC bullets currently marketed. That seems to be the more certain way of ending up with a disappointing rifle.